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In the "Life and Letters of Charles Darwin," edited by his son, Mr. Francis Darwin (volume 3 page 188), the following passage occurs:—
"In the spring of this year (1874) he read a book which gave him great pleasure, and of which he often spoke with admiration, "The Naturalist in Nicaragua," by the late Thomas Belt. Mr. Belt, whose untimely death may well be deplored by naturalists, was by profession an engineer, so that all his admirable observations in natural history, in Nicaragua and elsewhere, were the fruit of his leisure. The book is direct and vivid in style, and is full of description and suggestive discussions. With reference to it my father wrote to Sir J.D. Hooker: 'Belt I have read, and I am delighted that you like it so much; it appears to me the best of all natural history journals which have ever been published.'"
Now that the book so highly recommended by such an authority is about to be introduced to a public which has hitherto only known it by hearsay, it will be interesting to inquire into the reason of its appreciation by such men as Darwin and Hooker—and Lyell, Huxley, and Wallace, with other leaders of the scientific world of that day, might be quoted to the same effect—and to give some particulars of the author's short active life.
The Belts were an old family which had been established at Bossal in Yorkshire since the reign of Richard II. The main line died out some twenty years ago, but about the beginning of the eighteenth century a member of the family went to the Tyne to join the well-known ironworks of Crawley at Winlaton. He and his descendants remained with the firm for over a century, and he was the great-great-grandfather of the grandfather of Thomas Belt born at Newcastle-on-Tyne on November 27, 1832.
Thomas was the fourth child of a family of seven. His mother possessed a singularly sweet and beautiful disposition; his father, much given to hobbies, was stern and unbending, and he himself combined an almost womanly gentleness with a quiet determination that unflinchingly faced all obstacles. With a high sense of personal honour, unassuming and even-tempered, he was only roused to anger by acts of oppression or wanton cruelty. Then his indignation, though not loud, was very real, and he acted with a promptitude which would hardly have been expected from his usually placid demeanour. A story is told of how one day sitting at table he saw through the window a man belabouring a woman. Without saying a word, he rushed out, pinioned the offender by the elbows and, running him to the top of a steep slope in the street, gave him a kick which sent him flying down the declivity. The incident is recalled merely as an illustration of his practical way of dealing with difficulties which stood him in good stead in many an out-of-the-way corner of the world when contending with obstacles caused either by the perversity of man or the forces of nature. He never carried fire-arms even when travelling in the most unsettled districts, and his firm but conciliatory manner overcame opposition in a wonderful way. In ordinary life he was the kindest and most considerate of men, and his transparent sincerity made friends for him everywhere. Nor was he ever happier than when assisting others in those pursuits which occupied his own leisure.
The interesting question as to what led Belt to become a naturalist is difficult to answer.
"Environment" nowadays accounts for much, but none of his brothers—and all the family had a similar bringing-up—showed any inclination for what with him became the ruling passion of his life. And yet, in a wider sense, "environment" had probably something to do with it. In the first half of the nineteenth century Newcastle could boast of a succession of field-naturalists unequalled in the country—Joshua Alder and Albany Hancock, who wrote the monograph on British nudibranchiate mollusca for the Ray Society; William Hutton and John Thornhill, botanists; W.C. Hewitson, Dr. D. Embleton, and John Hancock, zoologists; Thomas Athey and Richard Howse, palaeontologists—these, and others like them, were enthusiastically at work collecting, observing, recording, classifying. Fresh discoveries were being made every day; what are now commonplace scientific truisms wore then all the charm of novelty; the secrets of nature were being unveiled, and modern science was entering upon an ever-extending kingdom.
Into all this scientific activity Belt was born, and from his earliest years it may be said of him, as in the well-known lines it was said of Agassiz:—
"And he wandered away and away With Nature, the dear old nurse, Who sang to him night and day The rhymes of the universe."
"And whenever the way seemed long, Or his heart began to fail, She would sing a more wonderful song, Or tell a more marvellous tale."
"If happiness," he wrote in his twenty-second year, "consists in the number of pleasing emotions that occupy our mind—how true is it that the contemplation of nature, which always gives rise to these emotions, is one of the great sources of happiness."
The earliest instance which has been remembered of his fondness for animal life occurred when he was about three years old. He had been in the garden and came running to show his mother what he had found. Opening his carefully gathered up pinafore, out jumped two frogs—to the great dismay of the good lady, for frogs are first cousins to toads, the dire effects of whose glance and venom were known to every one.
He received the best education the town could give, and was fortunate in his schoolmasters—first Dr. J.C. Bruce of antiquarian fame, and then Mr. John Storey, second to none in his day as a north-country botanist.
Belt's father was much interested in horticulture; and, possessing some meteorological instruments, entrusted him, when only twelve years old, with the keeping of a set of observations which showed not only the barometric and thermometric readings twice a day, and the highest and lowest temperatures, but also the rainfall, the state of the sky, the form of the clouds, and the force and direction of the wind. The elaborately arranged columns, full of symbols and figures, look very quaint in the careful boyish handwriting, and must have absorbed much of his spare time.
Insects, however, had the greatest attraction for him. He writes in his journal: "I have made a great improvement in the study of entomology, to which I have an ardent attachment." And a little later: "I find I have not time to study so many things. I am afraid that I will not be able to carry on entomology and botany together; but entomology I will not give up." He had been studying "electricity, astronomy, botany, conchology, and geology." At the age of sixteen he wrote: "I feel a longing, a natural desire, to explore and understand the ways of science. I am ambitious of doing something that will deserve the praise or excite the admiration of mankind." When the praise and admiration came, no one could have been more indifferent to them than himself. Nature, his "nurse," had become his queen; and never was there a more devoted, whole-hearted subject, a more simple-minded follower of science for its own sake without any thought of the honour or glory that might accrue thereby.
On August 10, 1849, he records: "I have been thinking for the last few days about fixing on some subject or pursuit on which to devote my life, as it is of no use first starting one subject and then another, thus learning nothing. After giving it a good deal of consideration, I have determined on studying 'Natural History,' not confining myself to any one branch of that vast subject. As this is a subject on which I intend to devote my leisure hours during the greater part if not the whole of my lifetime, I consider it to be of the greatest importance that I should lay a good foundation for it. I therefore intend during the ensuing winter to study the English language and composition, so as to be able to describe objects and explain my sentiments with greater clearness and precision than I can at present." The last sentence illustrates the systematic thoroughness of all his work which was one reason of his success.
Belt's "leisure hours" were soon more numerous than he had anticipated when recording his determination to devote them to natural history. Already his health had shown signs of giving way, and presently there was a nervous break-down which necessitated his giving up all work and being out in the open air as much as possible. But what appeared to be probably the wrecking of his life provided the opportunity which might not otherwise have occurred of encouraging and developing his inborn love of nature. Becoming a member of the Tyneside Naturalists' Field Club, he interested himself greatly in the local fauna and flora, and formed very complete collections of the plants, insects, and shells. His name occurs frequently in the "Transactions" of the Club as the recorder of species new to the district. His health gradually improved, but it was doubtful whether he would be able to bear the strain of any indoor occupation, for which indeed he felt an ever-increasing aversion.
It was the time of the discovery of gold in Australia, and after much discussion he and his elder brother joined the stream of adventurers and sailed in 1852 for Victoria. In this rough "school of mines" he acquired that insight into the building-up of the earth's crust and that practical knowledge of minerals which served him so well in after-life as a mining engineer. But although the whole colony was in the grip of the gold-fever, Belt retained the same quiet habits of observation which had marked him at home—for there, as to whatever part of the world his work subsequently called him, the engineer was always at heart a naturalist. He proved an excellent observer, and a certain speculative tendency led him to group his observations so as to bring out their full theoretical bearing.
Amid real hard work he found time to evolve a theory of whirlwinds and to speculate upon the soaring of birds. A companion has recorded in the following terms another matter which engaged much of his attention at this time: "The boldest of his speculations, and one of the soundest, as after-events proved, was his plan for crossing the Australian continent. He proposed, at the time the government expedition was mooted, to replace the costly plans of the government by the following scheme:—That he and his brother Anthony (who was unfortunately lost in the "Royal Charter") should be conveyed to the Gulf of Carpentaria, with about twenty pack-horses loaded with provisions and water; that an escort should protect them for some twenty miles from the coast, and that then the two voyagers only, with their pack-horses, should make their way to Cooper's Creek, the farthest known accessible point from the Victorian settled districts. Belt argued justly: 'If we fail, only two lives will be lost, but all chances are in our favour; we are provided with water and food more than ample to cover the distance we have to travel. Every step of our road carries us homeward and to safety. If we never find a drop of water on the road, our animals have enough to carry those who have to bear the whole journey to their goal, and as the animals succumb they will be shot or turned adrift.'
The event showed Belt's sagacity. The unfortunate government expedition left Melbourne loaded with camp-followers and impedimenta, and by the time they reached a few stages beyond Cooper's Creek were well-nigh exhausted. Burke, the leader of the expedition, in desperation started with his two men, Wills and King, and bravely struck out for the Gulf of Carpentaria. Through desert and fertile plains, not altogether destitute of water, they reached in safety the northern shore of Australia; but the energy, the courage, and the strength that took them this long, weary journey did not suffice to carry them back over double the distance to their camp. Brave hearts! they struggled on; but King only, and as a worn-out man, ever saw Cooper's Creek again. Belt's plan would have solved the problem without loss of life and at a tenth of the cost." He always regretted that he had not the means of carrying it out independently of government assistance.
After eight years in Australia Belt returned to England, married, and was successively manager of mining companies in Nova Scotia, North Wales, and Nicaragua, sandwiching in between these appointments a visit to Brazil to report upon some gold mines in the province of Maranham. In whatever part of the world his work took him he turned for rest and relaxation to the branches of natural science for which the locality offered the greatest opportunity.
In Nova Scotia he began those investigations into the cause and phenomena of the glacial period which were to be the study of the last years of his life, and to which he himself attached the greatest importance. In Wales he took up the question of the age of the rocks in the neighbourhood of Dolgelly, and after much study of their fossils proposed the now accepted classification of the Lingula flags of the Lower Silurian system into the Maenturog flags and slates, the Festiniog flags, and the Dolgelly slates. The collecting of lepidoptera was his chief amusement in Brazil, where he made his first acquaintance with the teeming life of the torrid zone and laid the foundation for those observations on tropical nature which his longer stay in Nicaragua gave rise to, and which are recorded in this book.
After his return from Central America, his services were in great request as a consulting mining engineer, and the succeeding years of his life were spent in almost continual travel: over all parts of Great Britain, to North and South Russia, Siberia, the Kirghiz Steppes, Mexico, and the United States. It was on one of his annual visits to Colorado that he was seized with sudden sickness and died on September 21, 1878, at the early age of forty-five.
Thomas Belt was an accurate and intelligent observer possessed of the valuable faculty of wonder at whatever is new or strange or beautiful in nature, and the equally valuable habit of seeking a reason for all he saw. Having found or imagined one, he went on to make fresh observations, and sought out new facts to see how they accorded with his supposed cause of the phenomena. "The Naturalist in Nicaragua" has therefore a value and a charm quite independent of the particular district it describes. As a mere book of travel it is surpassed by scores of other works. The country and the people of Nicaragua are too much like other parts of tropical Spanish America, with their dull, lazy inhabitants, to possess any novelty. There is little in the book that can be called adventure, and still less of geographical discovery.
And yet, the many and highly diversified phases in which life presents itself in the tropics enabled the skilled naturalist to fill a volume with a series of episodes, experiences, and speculations of which the reader will never tire. His keen powers of observation and active intellect were applied to various branches of scientific inquiry with unflagging ardour; and he had the faculty of putting the results of these inquiries in a clear, direct form, rendered the more attractive by its simplicity and absence of any effort at fine writing. He does not obtrude his own personality, and, like all genuine men, he forgets "self" over his subject. Instead of informing us whether or not he received "the salary of an ambassador and the treatment of a gentleman," he scatters before us, broadcast, facts interesting and novel, valuable hints for future research, and generalisations which amply repay a close study. Not alone the zoologist, the geologist, but the antiquarian, the ethnologist, the social philosopher, and the meteorologist will each find in these pages additions to his store of knowledge and abundant material for study.
With all this, the work is not a mere catalogue of dry facts: it is eminently a readable book, bringing vividly before us the various subjects with which it is concerned. Minutely accurate in his description of facts and bold in his reasoning upon them, Belt covered so much ground that some of his theories have not held their own; but others have stood the test of time and been absorbed into the world's stock of knowledge, while all bear witness to the singular grasp of his mind and have stimulated thought and observation—which is a great virtue in theories, be they true or false.
It has been already stated that Belt devoted the scanty leisure of his last years to the study of the glacial period, entering with zest into the consideration of its cause, the method of deposition of its beds, and the time-relationship of man to it—complex questions on which his imagination had full scope, and which, had his life been prolonged, his patient accumulation of evidence might have ultimately led him to suggest answers that would have been generally accepted by scientific men. But the cause of the remarkable change of climate during those late Tertiary and post-Tertiary times known as the glacial period is still without a completely satisfactory explanation. In Belt's day geologists were inclined to get over the difficulty of accounting for the phenomena by any feasible terrestrial change by explaining them as the result of cosmical causes, and Croll's theory of the increase of the eccentricity of the earth's orbit was widely received among them. Belt, on the other hand, held that the cold was due to an increase in the obliquity of the ecliptic. But these astronomical explanations have not met with much acceptance by physicists; and so chemists have been turned to by some geologists for support of the hypothesis of the variation in the amount of carbon dioxide in the air, or of other alterations in the atmosphere, while others have gone back to the idea of geographical changes. That considerable oscillations of the relative levels of land and sea took place during the Ice Age has been now clearly established, and the general result of the investigations favours Belt's opinion that the land during part of that period stood much higher than now over the northern regions of Europe and North America. It would, however, lead us too far away from the present book to enter into even a cursory examination of his views upon the glacial period, and those readers who desire to pursue the matter will find assistance for doing so in the bibliography at the end of this Introduction.
Of more immediate interest to us are the "observations on animals and plants in reference to the theory of evolution of living forms" which the title-page announces as a part of the narrative, and which indeed form the main portion of the work. Upon the publication of Darwin's "Origin of Species" in 1859, Belt had become an ardent evolutionist, and was henceforth always on the look-out for facts in support of the theories which had breathed such new life into biological studies. In Nicaragua he devoted special attention to those wonderful protective resemblances, especially among insects, which Bates had explained by his theory of "Mimicry;" and as the subject crops up again and again in this book, the non-scientific reader will find it helpful to have before him an outline of the expanded and completed theory—though he should be warned that some writers have been too much inclined to attribute to "mimicry" any accidental resemblance between two species. How far such accidental resemblances may be carried is probably well illustrated by the bee, the spider, and the fly orchis of our own downs and copses.
"Mimicry" proper is often confused with "protective resemblance," and it will be advisable to begin with the consideration of the latter.
Concealment, while useful at times to all animals, is absolutely essential to some; and it is wonderful in what different ways it is attained. In cases of "cryptic resemblance to surroundings" the shape, colouration, or markings are such as to conceal an animal by rendering it difficult to distinguish from its immediate environment. In most cases the effect is PROTECTIVE; but in snakes, spiders, mantids, and other preying animals it is termed AGGRESSIVE, since it enables these animals to stalk their prey undetected. It is probable that this power, when possessed by a vertebrate animal, nearly always bears the double meaning, as in the green tree frog, where the colouration is protective so far as it provides concealment from snakes, which are particularly fond of these frogs, and aggressive in that it allows flies and other insects to approach without suspicion.
There may be either General Resemblance to surrounding objects or Special Resemblance to definite objects. The plain sandy colour of desert animals, the snow white of the inhabitants of the arctic regions, the inconspicuous hues of nocturnal animals, the stripes of the tiger and the zebra, the spots of the leopard and the giraffe have all a cryptic effect which at a very short distance renders the creatures invisible amid their natural surroundings. Nor is it necessary in order to attain this invisibility that the colouring should be really dull and plain. It all depends upon the habitat. Mr. Wallace has described "a South American goatsucker which rests in the bright sunshine on little bare rocky islets in the upper Rio Negro where its unusually light colours so closely resemble those of the rock and sand that it can scarcely be detected till trodden upon." A little observation will supply large numbers of instances of such protective colouration.
It is, however, in the insect world that this principle of adaptation of animals to their environment is most fully and strikingly developed. "There are thousands of species of insects," says Mr. Wallace again, "which rest during the day clinging to the bark of dead or fallen trees; and the greater portion of these are delicately mottled with grey and brown tints, which though symmetrically disposed and infinitely varied, yet blend so completely with the usual colours of the bark, that at two or three feet distance they are quite undistinguishable."
In protective resemblances at their highest state of perfection the colouring is not constant but, as Professor Poulton puts it in his delightful book on "The Colours of Animals", "can be adjusted to harmonise with changes in the environment or to correspond with the differences between the environment of different individuals." The seasonal change of colour in northern animals is a well-known instance of the former, and the chameleon's alterations of hue of the latter.
Besides General Resemblance, in which the general effects of surrounding colours are reproduced, we have Special Resemblance, in which the appearance of a particular object is copied in shape and outline as well as in colour. Numerous instances will be found in this book, and a "Leaf Insect" and a "Moss Insect" are illustrated. But the classic example is the butterfly from the East Indies so graphically described by Mr. Wallace, Kallima paralekta, which always rests among dead or dry leaves and has itself leaf-like wings spotted over with specks to imitate the tiny fungi growths on the foliage it resembles. "It sits on a nearly upright twig, the wings fitting closely back to back, concealing the antennae and head, which are drawn up between their bases. The little tails of the hind wings touch the branch and form a perfect stalk to the leaf, which is supported in its place by the claws of the middle pair of feet which are slender and inconspicuous. The irregular outline of the wings gives exactly the perspective effect of a shrivelled leaf." The wonderful "stick insects" in like manner mimic the twigs of the trees among which they lurk. Nor need we go abroad in search of examples, for among our own insects are countless instances of marvellous resemblances to the inanimate or vegetable objects upon which they rest. One of the most interesting is that of the geometer caterpillars, which are very plentiful, and any one can observe them for himself even in a London garden. They support themselves for hours by means of their posterior legs, forming an angle of various degrees with the branch on which they are standing and looking for all the world like one of its twigs. The long cylindrical body is kept stiff and immovable, with the separations of the segments scarcely visible, and its colour is obscure and similar to that of the bark of the tree. Kirby and Spence tell of a gardener mistaking one of these caterpillars for a dead twig, and starting back in great alarm when, on attempting to break it off, he found it was a living animal.
Sometimes concealment is secured by the aid of adventitious objects. Many lepidopterous larvae live in cases made of the fragments of the substances upon which they feed; and certain sea-urchins cover themselves so completely with pebbles, shells, and so forth, that one can see nothing but a heap of little stones. Perhaps, however, the most interesting instance is the crab described by Mr. Bateson, which "takes a piece of weed in his two chelae and, neither snatching nor biting it, deliberately tears it across, as a man tears paper with his hands. He then puts one end of it into his mouth, and after chewing it up, presumably to soften it, takes it out in the chelae and rubs it firmly on his head or legs until it is caught by the peculiar curved hairs which cover them. If the piece of weed is not caught by the hairs, the crab puts it back in his mouth and chews it up again. The whole proceeding is most human and purposeful."
There is another class of colours in which not concealment but conspicuousness is the object aimed at. Such colours are borne by animals provided with formidable weapons of defence (the sting of the wasp, for example), or possessed of an unpleasant taste or offensive odour, and their foes come by experience to associate this form of colouring with disagreeable qualities and avoid the animals so marked. Belt was the first to account, in this way, for the conspicuous colouration of the skunk; and it is now believed that startling colours and conspicuous attitudes are intended to assist the education of enemies by enabling them to learn and remember the animals which are to be avoided. The explanation of warning colours was devised by Mr. Wallace to account for the brilliancy in the tints of certain caterpillars which birds find disagreeable, and the subject has been principally studied by experiments upon such caterpillars. But examples of warning colours are recognised, among many others, in the contrasted black and yellow of wasps, bees, and hornets, the bright red, black, and yellow bands of the deadly coral snakes, and the brilliantly coloured frog of Santo Domingo which hops unconcernedly about in the daytime in his livery of red and blue—"for nothing will eat him he well doth know."
But—and here comes in the principle to which the term "mimicry" is now restricted—if warning colours are helpful to noxious animals, then defenceless animals acquiring these colours will share in the protection afforded by them. And so we find a deceptive similarity between animals occurring in the same district, but not closely related, in which the mimicked form is unpalatable or has an odour repulsive to birds and lizards. It must, of course, be understood that the mimicry is unconscious, the result, as in the cases of cryptic resemblance, having been brought about by natural selection—the less perfect the mimicry the more liable are the individuals to be attacked, and the less chance have they of reproducing their kind.
This imitation was first accounted for by Mr. Bates in the case of the Heliconidae, a group of showy, slow-flying abundant butterflies possessing "a strong pungent semi-aromatic or medicinal odour which seems to pervade all the juices of their system." It does not follow, of course, that what seems to us a disagreeably smelling fluid should prove distasteful to the palate of a lizard or a bird. But careful observation of the butterflies convinced both Bates and Wallace that they were avoided, or at any rate not pursued, by birds and other creatures; and Belt found that they were rejected by his tame monkey which was very fond of other insects. So their conspicuous wings, with spots and patches of yellow, red, or white upon a black, blue or brown ground, may fairly be considered an example of warning colouration—though Mr. Thayer has with great ingenuity and acumen endeavoured to show that the markings are effective for concealment and that their value as warning marks is doubtful.
Now, says Mr. Beddard, "in the same situations as those in which the Heliconias are found there also occur, more rarely, specimens of butterflies minutely resembling the Heliconias, but belonging to a perfectly distinct family—the Pieridae. They belong to the two genera Leptalis and Euterpe, consisting of numerous species, each of which shows a striking likeness to some one particular species of Heliconia. This likeness is not a mark of near affinity; it affects no important character, but only the shape and colouration of the wings."
The particular resemblance here described was the origin of the theory of Protective Mimicry, the conditions under which it occurs being, according to Mr. Wallace:
1. That the imitative species occur in the same area and occupy the same station as the imitated. 2. That the imitators are always the more defenceless. 3. That the imitators are also less numerous in individuals. 4. That the imitators differ from the bulk of their allies. 5. That the imitation, however minute, is external and visible only, never extending to internal characters or to such as do not affect the external appearance.
There are plenty of examples of this phenomenon, such as the hornet-like moths and bee-like flies of our own country, and many other instances will be found in these pages. One discovered in tropical America by Mr. W.L. Sclater would have much delighted Belt had he come across it. In that region of the world the leaf-cutting ants present a very characteristic appearance as the column proceeds homewards, each ant carrying a piece of leaf held vertically in its jaws; and a homopterous insect has been found that faithfully resembles an ant bearing its burden. The latter is suggested by the thin compressed green body of the insect, and its profile is precisely like that of the jagged edge of the fragment of leaf held over the back of the ant.
Of all the Nicaraguan fauna, judging from the narrative, the ants occupy the most prominent position. Both indoors and out they are ever in evidence. Belt describes the foraging ants, which do not make regular nests of their own, but attack those of other species and prey upon every killable living thing that comes in their way; the leaf-cutting ants, whose attacks upon his garden were repelled with so much difficulty; standing armies of ants maintained by certain trees for their protection, and many other kinds, some of which kept his attention constantly on the stretch. Much space is devoted to their habits and wonderful instincts, amounting in many cases, so Belt considered, to as clear an evidence of reasoning intelligence as can be claimed for man himself. Indeed, after reading the account of their freeing of an imprisoned comrade and their grappling with problems arising out of such modern inventions as carbolic acid and tramways, we need not feel surprised if an observer accustomed to scrutinise the animal world so closely feels sceptical on the subject of "instinct" viewed as a mysterious entity antithetically opposed to "reason" and supposed to act as its substitute in the lower orders.
In reference to their methods of obtaining food, ants have been classified as hunting, pastoral, and agricultural, "three types," as Lord Avebury remarks, "offering a curious analogy to the three great phases in the history of human development." As regards their social condition they differ from mankind in having successfully established communism. At the present day all the social hymenoptera possess a unique interest on account of their working-order or neuters. These, as is well-known, are females whose normal development has been checked. Are we to assume that "once upon a time" a woman's rights movement sprang up in bee-hives and ant-hills which ended in reducing the males to a very unimportant position and in limiting the number of the fully developed females? Are we to expect that the "strong-minded" women arising among us are the forerunners of a "neuter" order and the heralds of a corresponding change in human society?
"It is full of theories," says the author, writing of his book; modestly adding, "I trust not unsupported by facts." And so naturally does he dovetail the two together that the theories often seem portions of the facts. On all kinds of subjects suggestive reasons are proposed:—why the scarlet-runners which flowered so profusely in his garden never produced a single pod; why the banana and sugar-cane are probably not indigenous to America; why gold veins grow poorer as they descend into the earth; why whirlwinds rotate in opposite directions in the two hemispheres; why the earthenware vessels of the Indians are rounded at the bottom and require to be placed in a little stand—on all the varied matters that come under his observant eyes he has something interesting to say. You learn how the natives obtain sugar, palm-wine, and rubber; what is the use of the toucan's huge beak, and how plants secure the fertilisation of their flowers. You watch the tricks of the monkey, the humming-bird's courtship, the lying in wait of the alligator, and all the ceaseless activity of the forest—that forest so monotonous in its general features, but fascinating beyond measure when the varied life-histories working out within it are realised—and you share in the keen joy of the naturalist who has written with such simple eloquence of the beauty, the wonder, and the mystery of the natural world.
"The rapid squirt of a proteinaceous slime jet endows the ancient velvet worms (Onychophora) with a unique mechanism for defense from predators and for capturing prey by entangling them in a disordered web that immobilizes their target. However, to date neither qualitative nor quantitative descriptions have been provided for this unique adaptation. Here we investigate the fast oscillatory motion of the oral papillae and the exiting liquid jet that oscillates with frequencies f∼30−60 Hz. Using anatomical images, high speed videography, theoretical analysis and a physical simulacrum we show that this fast oscillatory motion is the result of an elastohydrodynamic instability driven by the interplay between the elasticity of oral papillae and the fast unsteady flow during squirting. Our results demonstrate how passive strategies can be cleverly harnessed by organisms, while suggesting future oscillating micro-fluidic devices as well as novel ways for micro and nano fiber production using bioinspired strategies."
Interest rates around the world, both short-term and long-term, are exceptionally low these days. The U.S. government can borrow for ten years at a rate of about 1.9 percent, and for thirty years at about 2.5 percent. Rates in other industrial countries are even lower: For example, the yield on ten-year government bonds is now around 0.2 percent in Germany, 0.3 percent in Japan, and 1.6 percent in the United Kingdom. In Switzerland, the ten-year yield is currently slightly negative, meaning that lenders must pay the Swiss government to hold their money! The interest rates paid by businesses and households are relatively higher, primarily because of credit risk, but are still very low on an historical basis.
Low interest rates are not a short-term aberration, but part of a long-term trend. As the figure below shows, ten-year government bond yields in the United States were relatively low in the 1960s, rose to a peak above 15 percent in 1981, and have been declining ever since. That pattern is partly explained by the rise and fall of inflation, also shown in the figure. All else equal, investors demand higher yields when inflation is high to compensate them for the declining purchasing power of the dollars with which they expect to be repaid. But yields on inflation-protected bonds are also very low today; the real or inflation-adjusted return on lending to the U.S. government for five years is currently about minus 0.1 percent.
Why are interest rates so low? Will they remain low? What are the implications for the economy of low interest rates?
If you asked the person in the street, “Why are interest rates so low?”, he or she would likely answer that the Fed is keeping them low. That’s true only in a very narrow sense. The Fed does, of course, set the benchmark nominal short-term interest rate. The Fed’s policies are also the primary determinant of inflation and inflation expectations over the longer term, and inflation trends affect interest rates, as the figure above shows. But what matters most for the economy is the real, or inflation-adjusted, interest rate (the market, or nominal, interest rate minus the inflation rate). The real interest rate is most relevant for capital investment decisions, for example. The Fed’s ability to affect real rates of return, especially longer-term real rates, is transitory and limited. Except in the short run, real interest rates are determined by a wide range of economic factors, including prospects for economic growth—not by the Fed.
To understand why this is so, it helps to introduce the concept of the equilibrium real interest rate(sometimes called the Wicksellian interest rate, after the late-nineteenth- and early twentieth-century Swedish economist Knut Wicksell). The equilibrium interest rate is the real interest rate consistent with full employment of labor and capital resources, perhaps after some period of adjustment. Many factors affect the equilibrium rate, which can and does change over time. In a rapidly growing, dynamic economy, we would expect the equilibrium interest rate to be high, all else equal, reflecting the high prospective return on capital investments. In a slowly growing or recessionary economy, the equilibrium real rate is likely to be low, since investment opportunities are limited and relatively unprofitable. Government spending and taxation policies also affect the equilibrium real rate: Large deficits will tend to increase the equilibrium real rate (again, all else equal), because government borrowing diverts savings away from private investment.
If the Fed wants to see full employment of capital and labor resources (which, of course, it does), then its task amounts to using its influence over market interest rates to push those rates toward levels consistent with the equilibrium rate, or—more realistically—its best estimate of the equilibrium rate, which is not directly observable. If the Fed were to try to keep market rates persistently too high, relative to the equilibrium rate, the economy would slow (perhaps falling into recession), because capital investments (and other long-lived purchases, like consumer durables) are unattractive when the cost of borrowing set by the Fed exceeds the potential return on those investments. Similarly, if the Fed were to push market rates too low, below the levels consistent with the equilibrium rate, the economy would eventually overheat, leading to inflation—also an unsustainable and undesirable situation. The bottom line is that the state of the economy, not the Fed, ultimately determines the real rate of return attainable by savers and investors. The Fed influences market rates but not in an unconstrained way; if it seeks a healthy economy, then it must try to push market rates toward levels consistent with the underlying equilibrium rate.
This sounds very textbook-y, but failure to understand this point has led to some confused critiques of Fed policy. When I was chairman, more than one legislator accused me and my colleagues on the Fed’s policy-setting Federal Open Market Committee of “throwing seniors under the bus” (to use the words of one senator) by keeping interest rates low. The legislators were concerned about retirees living off their savings and able to obtain only very low rates of return on those savings.
I was concerned about those seniors as well. But if the goal was for retirees to enjoy sustainably higher real returns, then the Fed’s raising interest rates prematurely would have been exactly the wrong thing to do. In the weak (but recovering) economy of the past few years, all indications are that the equilibrium real interest rate has been exceptionally low, probably negative. A premature increase in interest rates engineered by the Fed would therefore have likely led after a short time to an economic slowdown and, consequently, lower returns on capital investments. The slowing economy in turn would have forced the Fed to capitulate and reduce market interest rates again. This is hardly a hypothetical scenario: In recent years, several major central banks have prematurely raised interest rates, only to be forced by a worsening economy to backpedal and retract the increases. Ultimately, the best way to improve the returns attainable by savers was to do what the Fed actually did: keep rates low (closer to the low equilibrium rate), so that the economy could recover and more quickly reach the point of producing healthier investment returns.
A similarly confused criticism often heard is that the Fed is somehow distorting financial markets and investment decisions by keeping interest rates “artificially low.” Contrary to what sometimes seems to be alleged, the Fed cannot somehow withdraw and leave interest rates to be determined by “the markets.” The Fed’s actions determine the money supply and thus short-term interest rates; it has no choice but to set the short-term interest rate somewhere. So where should that be? The best strategy for the Fed I can think of is to set rates at a level consistent with the healthy operation of the economy over the medium term, that is, at the (today, low) equilibrium rate. There is absolutely nothing artificial about that! Of course, it’s legitimate to argue about where the equilibrium rate actually is at a given time, a debate that Fed policymakers engage in at their every meeting. But that doesn’t seem to be the source of the criticism.
The state of the economy, not the Fed, is the ultimate determinant of the sustainable level of real returns. This helps explain why real interest rates are low throughout the industrialized world, not just in the United States. What features of the economic landscape are the ultimate sources of today’s low real rates? I’ll tackle that in later posts.
"We study the imprint of new particles on the primordial cosmological fluctuations. New particles with masses comparable to the Hubble scale produce a distinctive signature on the non-gaussianities. This feature arises in the squeezed limit of the correlation functions of primordial fluctuations. It consists of particular power law, or oscillatory, behavior that contains information about the masses of new particles. There is an angular dependence that gives information about the spin. We also have a relative phase that crucially depends on the quantum mechanical nature of the fluctuations and can be viewed as arising from the interference between two processes. While some of these features were noted before in the context of specific inflationary scenarios, here we give a general description emphasizing the role of symmetries in determining the final result."
"Ground-based observatories have been collecting 0.2-20 TeV gamma rays from blazars for about twenty years. These gamma rays can experience absorption along the line of sight due to interactions with the extragalactic background light (EBL). In this paper, we investigate the most extensive set of TeV spectra from blazars collected so far, twice as large as any other studied. We first show that the gamma-ray optical depth can be reduced to the convolution product of an EBL kernel with the EBL intensity. We extract the EBL intensity from the gamma-ray spectra, show that it is preferred at 11 sigma to a null intensity, and unveil the broad-band spectrum of the EBL from mid-UV to far IR. Our measurement shows that the total radiative content of the universe between 0.1 and 1000 microns represents 6.5+/-1.2% of the brightness of the CMB. This is slightly above the accumulated emission of stars and galaxies and constrains the unresolved sources that could have reionized the universe. We also propose a data-driven method to estimate the Hubble constant based on the comparison of local and gamma-ray measurements of the EBL, yielding H0 = 88 +/- 8(stat) +/-13(sys) km/s/Mpc. After setting the most stringent upper-limits on the redshift of four TeV blazars, we investigate the 106 intrinsic gamma-ray spectra in our sample and find no significant evidence for anomalies. We do not find evidence for the so-called "pair-production anomaly" at large optical depths, which has been used previously to place lower limits on the coupling of TeV gamma rays with axion-like particles. Finally, we investigate the impact of a modification of the pair-creation threshold due to a Lorentz invariance violation. A mild excess prevents us from ruling out an effect at the Planck energy and we constrain for the first time the energy scale of the modification to values larger than sixty percent of the Planck energy."
"It is the purpose of the present article to collect arguments for, that there should exist in fact -- although not necessarily yet found -- some law, which imply an adjustment to special features to occur in the future. In our own "complex action model" we suggest a version in which the "goal" according to which the future is being arranged is to diminish the integral over time and space of the numerical square of the Higgs field. We end by suggesting that optimistically calculated the collected evidences by coincidences runs to that the chance for getting so good agreement by accident would be of the order of only 1 in 30000. In addition we review that the cosmological constant being so small can be considered evidence for some influence backward in time. Anthropic principle may be considered a way of simulating influence backward in time."
"A model for the total photoproduction cross section based on the ansatz that resummation of infrared gluons limits the rise induced by QCD minijets in all the total cross-sections, is used to simulate extended air showers initiated by cosmic rays with the AIRES simulation program. The impact on common shower observables, especially those related with muon production, is analysed and compared with the corresponding results obtained with previous photoproduction models"
"For the first time a proper comparison of the average depth of shower maximum (Xmax) published by the Pierre Auger and Telescope Array Observatories is presented. The Xmax distributions measured by the Pierre Auger Observatory were fit using simulated events initiated by four primaries (proton, helium, nitrogen and iron). The primary abundances which best describe the Auger data were simulated through the Telescope Array (TA) Middle Drum (MD) fluorescence and surface detector array. The simulated events were analyzed by the TA Collaboration using the same procedure as applied to their data. The result is a simulated version of the Auger data as it would be observed by TA. This analysis allows a direct comparison of the evolution of ⟨Xmax⟩ with energy of both data sets. The ⟨Xmax⟩ measured by TA-MD is consistent with a preliminary simulation of the Auger data through the TA detector and the average difference between the two data sets was found to be (2.9±2.7(stat.)±18(syst.)) g/cm2."
"The design and performance of the GPS Timing and Control (GTC) System of the High Altitude Water Cerenkov (HAWC) gamma ray observatory is described. The GTC system provides a GPS synchronized absolute timestamp, with an accuracy better than 1μs, for each recorded event in HAWC. In order to avoid any slack between the recorded data and the timestamp, timestamps are injected to the main data acquisition (DAQ) system after the Front-end Electronic Boards (FEBs). When HAWC is completed, the HAWC main DAQ will use 10 time to digital converters (TDCs). In order to keep all the TDCs in sync, the GTC system provides a synchronized clock signal, coordinated trigger signal, and control signals to all TDCs."
Earth based accelerators, cannot give us all the reasons behind particle interactions. I remember that my UCSB thesis advisor, Robert L. Sugar told me in 1973, to look into the expanding proton phenomenon. Cosmic ray physics had shown us, that the probability for protons to collide INCREASES, as the energy increases beyond certain point. I was, and still am, very intrigued.
The first job in my life, was as a laboratory assistant, at the Mexican Nuclear Energy Commission in 1970. I was then a senior, at the department of Communications, and Electronics Engineering, at Escuela Superior de Ingeniería Mecánica y Eléctrica, of the Instituto Politécnico Nacional (IPN) in Mexico City. I worked at the Plasma Physics Laboratory. My boss, Mario Vázquez Reyna, under the direction of Manuel Sandoval Vallarta, a pioneer in Cosmic Ray Physics in Mexico, had built electronic detectors. I studied plasma magnetic confinement at the laboratory. During that year, I decided to study Physics instead of electronics. I did not want to build detectors for others, I wanted to propose the needed observations, to prove ideas in Physics.
The opportunity came along, in the field of cosmic rays, with the invitation to join the Pierre Auger Observatory in 1994. I was on a sabbatical leave from the Autonomous University of Puebla, at the Fermi National Laboratory in Batavia, Illinois, My professor Arnulfo Zepeda Domínguez, was invited, by the Nobel laureate James Cronin, from the University of Chicago, to join this international collaboration; and professor Zepeda invited me. The university in Puebla had very good conditions to join this effort. I was working at the Escuela de Ciencias Físco Matemáticas, which was started by professor Luis Rivera Terrazas, precisely to join international efforts in modern physics. There were Physics, Mathematics, Electronics, and Computer Science departments.
As soon as I went back to Puebla, I talked with my friend Alberto Cordero Dávila. With his experience at the Instituto Nacional de Astrofísica Óptica y Electrónica in the nearby town of Tonantzintla, he immediately proposed the kind of instrument to use for the light collecting part of the observatory, the Schmidt Camera, which was adopted by the collaboration.
There is a surface detector part of the Auger Observatory, working together with the optical one mentioned above. Here my friend, Humberto Salazar Ibargüen, took the initiave. Professor Salazar obtained his Ph.D. working at the General Relativity Group of professor Jerzy Plebanski, at the Centro de Investigación y de Estudios Avanzados of IPN. He addressed the many technical problems, to build water tank detectors, with Cherenkov phototubes.
The High Altitude Water Cherenkov Experiment or High Altitude Water Cherenkov Observatory (also known as HAWC) is a gamma-rayobservatory located on the flanks of the Sierra Negra volcano in the Mexican state of Puebla at an altitude of 4100 meters, at 18°59′41″N97°18′30.6″W. HAWC is the successor to the Milagro gamma-ray observatory in New Mexico, which was also a gamma-ray observatory based around the principle of detecting gamma-rays indirectly using the water Cherenkov method.
I am humbled by the work done by my friends in Mexico. Arnulfo Zepeda told me that Manuel Sandoval Vallarta, conveyed to him, his wish, that Cosmic Ray Physics in Mexico must continue. Professor Eduardo Piña Garza spent some time with us at Puebla. He had studied the motion of electrically charged particles in the Earth's magnetic field; continuing the work of Carlos Graef Fernández. I can attest to the high caliber of professor Piña, because I was fortunate to publish an article with him. Mario Vázquez Reyna, and Manuel Sandoval Vallarta, would've been as happy as I am, for the Mexican contribution to Cosmic Ray Physics.
With nearly 3,000 votes cast, the results of Prospect’s world thinkers 2015 poll are now in. Voters came to the Prospect website in large numbers through Twitter and Facebook, and from many countries around the world.
The top 10 of last year’s poll was dominated by thinkers—including the winner, economist and philosopher Amartya Sen—whose work focused on the social, political and environmental challenges posed by economic growth in the developing world. However, Sen and others, notably the economists Raghuram Rajan and Kaushik Basu, are absent from this year’s list, which rewards impact over the past 12 months. In their place in the top 10 are thinkers who are wrestling, in different ways, with the dysfunctions of what some persist in calling the “developed world.”
2014 was Thomas Piketty’s year—as of January 2015, his book Capital in the Twenty-First Century had sold a remarkable 1.5m copies worldwide in several languages—and this is reflected in the French economist’s position at the top of our list. The past year has also been one in which anxieties about the economic, social and political costs of inequality have moved up the political agenda.
Several of the other thinkers in the top 10—particularly Yanis Varoufakis, Naomi Klein, Paul Krugman and Russell Brand (whose inclusion on the original list of 50 attracted considerable media coverage,some of it even favourable)—share similar concerns. It is striking, too, that they are all, broadly speaking, on the political left. One economist who has spoken out against Piketty and in defence of the “1 per cent,” the American Greg Mankiw, came near the bottom of the poll.
As was the case last year, there are two women in the top 10, Klein and Arundhati Roy (in 2013, there were none). And the presence of Hilary Mantel, Rebecca Solnit and Mona Eltahawy in the top 20 suggests that feminist critique of various kinds is experiencing a resurgence.
Many thanks to all those who voted. Do let us know what you make of the results on Twitter @Prospect_UK or in the comments.
"Branko Milanovic notes Lee Kwan Yew’s explanation of the success of Singapore and other Asian economies; partly Confucian culture, partly air conditioning. If you’ve ever tried to walk around Singapore, you know whereof he speaks."
"PHILADELPHIA — For all its horrific power, the atom bomb — leveler of Hiroshima and instant killer of some 80,000 people — is but a pale cousin compared to another product of American ingenuity: the hydrogen bomb."
Given the historic low temperatures and snowfalls that pummeled the eastern U.S. this winter, it might be easy to overlook how devastating California's winter was as well.
As our “wet” season draws to a close, it is clear that the paltry rain and snowfall have done almost nothing to alleviate epic drought conditions. January was the driest in California since record-keeping began in 1895. Groundwater and snowpack levels are at all-time lows. We're not just up a creek without a paddle in California, we're losing the creek too.
Data from NASA satellites show that the total amount of water stored in the Sacramento and San Joaquin river basins — that is, all of the snow, river and reservoir water, water in soils and groundwater combined — was 34 million acre-feet below normal in 2014. That loss is nearly 1.5 times the capacity of Lake Mead, America's largest reservoir.
Statewide, we've been dropping more than 12 million acre-feet of total water yearly since 2011. Roughly two-thirds of these losses are attributable to groundwater pumping for agricultural irrigation in the Central Valley. Farmers have little choice but to pump more groundwater during droughts, especially when their surface water allocations have been slashed 80% to 100%. But these pumping rates are excessive and unsustainable. Wells are running dry. In some areas of the Central Valley, the land is sinking by one foot or more per year.
As difficult as it may be to face, the simple fact is that California is running out of water — and the problem started before our current drought. NASA data reveal that total water storage in California has been in steady decline since at least 2002, when satellite-based monitoring began, although groundwater depletion has been going on since the early 20th century.
Right now the state has only about one year of water supply left in its reservoirs, and our strategic backup supply, groundwater, is rapidly disappearing. California has no contingency plan for a persistent drought like this one (let alone a 20-plus-year mega-drought), except, apparently, staying in emergency mode and praying for rain.
In short, we have no paddle to navigate this crisis.
Several steps need be taken right now. First, immediate mandatory water rationing should be authorized across all of the state's water sectors, from domestic and municipal through agricultural and industrial. The Metropolitan Water District of Southern California is already considering water rationing by the summer unless conditions improve. There is no need for the rest of the state to hesitate. The public is ready. A recent Field Poll showed that 94% of Californians surveyed believe that the drought is serious, and that one-third support mandatory rationing.
Second, the implementation of the Sustainable Groundwater Management Act of 2014 should be accelerated. The law requires the formation of numerous, regional groundwater sustainability agencies by 2017. Then each agency must adopt a plan by 2022 and “achieve sustainability” 20 years after that. At that pace, it will be nearly 30 years before we even know what is working. By then, there may be no groundwater left to sustain.
Third, the state needs a task force of thought leaders that starts, right now, brainstorming to lay the groundwork for long-term water management strategies. Although several state task forces have been formed in response to the drought, none is focused on solving the long-term needs of a drought-prone, perennially water-stressed California.
Our state's water management is complex, but the technology and expertise exist to handle this harrowing future. It will require major changes in policy and infrastructure that could take decades to identify and act upon. Today, not tomorrow, is the time to begin.
Finally, the public must take ownership of this issue. This crisis belongs to all of us — not just to a handful of decision-makers. Water is our most important, commonly owned resource, but the public remains detached from discussions and decisions.
This process works just fine when water is in abundance. In times of crisis, however, we must demand that planning for California's water security be an honest, transparent and forward-looking process. Most important, we must make sure that there is in fact a plan.
Call me old-fashioned, but I'd like to live in a state that has a paddle so that it might also still have a creek. Jay Famiglietti is the senior water scientist at the NASA Jet Propulsion Laboratory/Caltech and a professor of Earth system science at UC Irvine. LaTimes