Page:Popular Science Monthly Volume 45.djvu/539

 Nature. Energy as considered in physics, apart from chemistry has been classified in various forms, viz., energy of motion (translation or rotation), strain, vibration, beat, radiation, electrification, electricity in motion, magnetization, and gravitative separation. Those forms which are represented directly by bodies (whether extended masses or molecules) in motion or deformation, and which do not appeal to our special senses for recognition, constitute mechanical energy. The first two named above are plainly such, and all the others except the last have been shown to be such indirectly; it is generally believed that the last will be found to be reducible to the same form, so that probably all are essentially mechanical, and physicists are hoping to reduce them all to the mechanical as the ultimate form of energy. The importance to the physicist, therefore, of an acquaintance with the principles of mechanics can not be overestimated: without such an acquaintance his efforts to unravel the mysteries of physical science or to gain possession of its secrets will be futile.



N the first glance over Nature, everything living, every plant or animal, and every part of what lives, seems to have a definite shape; and we are naturally led to regard form in organized beings as an essential attribute of life. On the other hand, gases, which spread out into infinity; liquids, molding themselves on the walls of the vessels that stop their flow; rocks, cut into a thousand shapes without ceasing to be the same rock—show us an inorganic world almost wholly freed from the fatality of form. Crystals, indeed, seem to form an exception to this. They also have limited shapes, with contours even much better defined than those of life; but when we bray them in a mortar, they are still always the same body, and the same chemical species, even though they are no longer crystals. A living being, sugar cane or beet root, rasped or reduced to pulp, has no longer anything of itself. It has ceased to be, and no power can, from the pulp, build the organism back into its former shape. But we can reconstruct the crystal, and draw it anew from its dust.

The living being, considered in itself, independently of the being from which it is derived and those which will be derived from it, is, in its way, with some exceptions, a sort of atom, an indivisible whole. Hence that very just denomination of individual, to designate the being endowed with life.

What we call species in speaking of plants and animals is 