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Show z INTRODUCTION. other. the combinations or separations which re~ult from the ene:al tendency of these mole~ules to re-umte; and th~ ~odifications which the various clrcumstances capable of se paratm. g or approxt.m a t"1 ng them produce on that t. endency. It is purely a science of experiment, and is irreductble to ca1 c u- Iation. · · b 1 · ther to The theory of heat and that of electriCity . e ong ei. . dynamics or chemistry' according to the pomt of vtew m which they are considered. . The ruling method in all the branches of gene~al physics consists in isolating bodies, reducing them to thetr grea.test simplicity' in bringing each of their ~roperties separately I~ to action, either by reflection or experr~nent, and. ~y observmg or calculating the results; and finally, tn generahsmg and connecting the laws of these properties, so as t? form .co~es, and, if it were possible, to refer them to one smgle prmCiple into which they might all be resolved. . The object of Particulm· Physics, or of N~tural:f!zst.oryfor the terms are synonymous-is the special apphcatwn of the laws recognised by the various branc~es of .ge~eral phy· sics to the numerous and varied beings Whtch extst tn nature, in order to explain the phenomena which each of them pre· ~~. . Within this extensive range, astronomy also would be .m· eluded; but that science, sufficiently elucidated by mech~mcs, and completely subjected to its laws, employs. m~thods, d1ffer· ing too widely from those required by natural htstory, to per· mit it to be cultivated by the students of the latter. Natural history, then, is confined to objects which do not allow of exact calculation, nor of precise measurement in all their parts. Meteorology also is substract~d fr~m it a~d united to general physics; so that, properly speakmg,.tt constd~rs only inanimate bodies called minerals, and the different kmds of living beings, in all of which we may observe th: effects, ~ore or less various, of the laws of motion and chemical attraction, and of all the other causes analysed by general physics. Natural history, in strictness, should employ similar methods with the general sciences; and it does so, in fact, whenever the INTRODUCTION. 3 objects it examines are sufficiently simple to allow it. This, however, is but very rarely the case. An essential difference between the general sciences and natural history is, that in the former, phenomena are examined, whose conditions are all regulated by the examiner, in order, by their analysis, to arrive at general laws; whereas in the latter, they take place under circumstances beyond the control of him who studies them for the purpose of discovering amid the complication, the effects of known general laws. He is not, like the experimenter, allowed to subtract them successively from each condition, and to reduce the problem to its elements-he is compelled to take it in its entireness, with all its conditions at once, and can perform the analysis only in thought. Suppose, for example, we attempt to insulate the numerous phenomena which compose the life of any of the higher orders of animals; a single one being suppressed, every vestige of life is annihilated. Dynamics have thus nearly become a science of pure calculation ; chemistry is still a science of pure experiment ; and natural history, in a great number of its branches, will long remain one of pure observation. These three terms sufficiently designate the methods employed in the three branches of the natural sciences; but in establishing between them very different degrees of certitude, they indicate, at the same time, the point to which they should incessantly tend, in order to attain nearer and nearer to perfection. Calculation, if we may so express it, thus commands nature, and determines her phenomena more exactly than observation can make them known; experiment compels her to unveil; while observation pries into her secrets when refractory, and endeavours to surprise her. There is, however, a principle peculiar to natural history, which it uses with advantage on many occasions; it is that of the conditions of existence, ~ommonly styled final causes. As nothing can exist without the re-union of those conditions which render its existence possible, the component parts of each being must be so arranged as to render possible the whole |