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In Great Britain his fame seems to rest almost entirely on his peculiar scheme of graduating the thermometer. He chose the extreme points of the freezing and boiling of water, which, under similar circumstances, are always fixed and unvarying. The interval between these points he divided into eighty degrees, upon the principle that spirit of wine, in a certain state of rectification, expands 80,000 parts. In his experiments on this subject he arrived at some valuable conclusions, in regard to the varieties in their volume and temperature which are exhibited by particular fluids when combined, as well as on frigorific mixtures. He also carefully collected the observations on heat made in different places by means of his thermometer.

The importance and utility of these researches[Pg 187] are unquestionable, and yet there is even more of novelty and interest in those which he made in natural history. For instance, he explained the means by which many shells, sea-stars, and other mollusca or zoophytes, execute their progressive motion. He likewise illustrated the curious manner in which the claws of crabs and lobsters are reproduced. He also threw a new light on the singular action of the torpedo, and the organ by means of which it is exercised, although the phenomena of electricity were not then sufficiently understood to enable him to perceive all the relations of his subject. In 1718, he published a memoir on the rivers of France, which contain grains of gold in their sands, and soon after described the immense beds of fossil shells known in Touraine under the name of falun. In 1723, he made observations on the lustre emitted by several kinds of shell-fish, especially the pholades, which perforate wood and stones.

Physiology is indebted to him for the ingenious and decisive experiments which, in 1752, made known the difference that exists, with respect to digestion, between birds of prey, whose stomach acts on their food only by means of a solvent fluid, and granivorous birds, in which a very powerful muscular gizzard exercises a pressure sufficient to break down the hardest bodies and reduce them to powder.

These labours might well have sufficed for a single life; but the most remarkable undertaking of Reaumur has not yet been mentioned. It is entitled Memoires pour servir à l'Histoire des Insectes, and extends to six quarto volumes, which[Pg 188] were published between 1734 and 1742. This work occupied many years, and was the result of numerous observations made principally in his own garden, where he kept insects of all kinds, for the purpose of examining their habits, changes, and generation. It is, however, incomplete,—the locusts and grashoppers, as well as the whole tribe of coleoptera, having been intended for subsequent volumes, which never appeared.

In regard to these Memoires, he remarks, that although he has endeavoured to give them some degree of connexion, they might for the most part be considered as independent of each other; and that his object was not to present a systematic description of insects, but to furnish materials for the use of future naturalists. It is therefore improper to say, that he wrote his work with an entire contempt of method; and certainly the notices which he collected must have required more time and talent than the mere arrangement of insects according to characters derived from their external form. "The number of observations necessary for a tolerably complete history of so many minute animals," he says, "is prodigious. When one reflects on all that an accomplished botanist ought to know, it is enough to frighten him. His memory is loaded with the names of twelve or thirteen thousand plants, and he is expected to be able to recall on occasion the image of any one of them. There is perhaps none of these plants that has not insects peculiar to itself; and some trees, such as the oak, give sustenance to several hundreds of different species. And, after all, how many are there that do not live[Pg 189] on plants! How many species that devour others! How many that live at the expense of larger animals, on which they feed continually! How many species are there, some of which pass the greater part of their time in water, while others pass it entirely there! The immensity of Nature's works is nowhere more apparent than in the prodigious multiplicity of these species of little animals." He then proceeds to remark, that, as it is impossible for one man to acquire a knowledge of all the insects of even a limited district, and as thousands of minute insects must for ever remain unknown to us, instead of burdening our memory with the characteristic distinctions of these creatures, and thus preventing ourselves from attending to matters of more importance, it would be sufficient for us to know the principal genera, and especially those that are of most frequent occurrence, and to make ourselves acquainted with their peculiarities, their food, their propagation, the different forms which they assume in the course of their life, and such like circumstances. He avows that he had no great regard for a precise enumeration of the species of each genus; holding it enough to distinguish the more remarkable.

"Although," he continues, "we would greatly restrict the limits of the study, there are persons who will think them still too wide; there are even some who consider all knowledge of this part of natural history as useless, and who unhesitatingly pronounce it a frivolous amusement. We are equally willing that these pursuits should be regarded as amusements, that is, as studies which, so far from being troublesome,[Pg 190] afford pleasure to the person who engages in them. They do more,—they necessarily raise the mind to admire the Author of so many wonders. Ought we to be ashamed of ranking among our occupations observations and researches, of which the object is an acquaintance with the works on which the Supreme Being has displayed a boundless wisdom, and varied to such a degree? Natural history is the history of his works; nor is there any demonstration of his existence more intelligible to all men than that which it furnishes."

The two first volumes treat of caterpillars, their forms and habits, their metamorphoses into butterflies, and the insects which attack them, or which live within their bodies. The third speaks of the small creatures named moths, which exist in the interior of the substances which they devour, or form of them coverings for their protection. It also contains the history of the aphides, a very numerous race of small insects, which suck the juices of trees and plants, live in society, and are often productive of great damage. These animalcules are especially remarkable for their mode of generation; it having been proved by M. Bonnet, that a single impregnation is sufficient for the production of many successive generations, and that they are viviparous in summer and oviparous in autumn. The flies which produce the excrescences named gall-nuts, and the worms from which come the dipterous insects, so diversified in their forms, manners, and places of abode, occupy the fourth volume. The fifth contains, among other genera, the bees, of which the history is so singular and interesting.[Pg 191] Certain varieties of these as well as wasps are described in the last volume. Similar researches were made by Bonnet and De Geer, of whom we shall have occasion to speak in another part of our series.

Reaumur was the first naturalist who formed an extensive collection of animals in France. The celebrated Brisson, who was the keeper of his museum, derived from it the principal materials for his works on quadrupeds and birds. These last afterwards constituted the basis of the Royal Museum at Paris.