Organic nature to the modern interpreter is thus alive through and through. In his view atom and molecule are also alive in a subordinate, elemental degree. Indeed, he thinks, it is their life borne in air, water and food which in plant or animal rises to new planes of dignity. He looks afresh at the broken alum crystal which repairs itself in a solution, and sees there the removal of the imaginary fence which long divided organic nature from inorganic. (See illustration, page 194.) It was a shrewd guess of Sir Isaac Newton that the diamond is combustible; he did not suspect it to be carbon, but he knew it to be highly refrangible as are many combustible bodies. His conjecture shows him taking the first step toward the current view that properties, the modes of behavior of matter, are not passive qualities, but are due to real activities; that what a substance is depends upon how its ultimate parts move. Clausius and Maxwell in a theory which marks a new era explained the elasticity of gases as manifested in the ceaseless motion of their molecules, declaring that an ounce of air within a fragile jar is able to sustain the pressure of the atmosphere around it, because the air, though only an ounce in weight, dashes against its container with an impact forcible enough to balance the external pressure. Proof whereof appears in measuring the velocity of air as it rushes into a vacuum. Here a significant point is that in leaving the realm of mass-mechanics, where the tax of friction is inexorable, we enter a sphere where the swiftest motion may go on forever without paying friction the smallest levy.
Elasticity of solids is explained on the same principle. If we swiftly turn a gyroscopic wheel we can only change its plane of rotation by an effort, which effort is repaid when the metal is allowed to resume its original plane of motion. It is imagined that in like manner the particles in an elastic spring move rapidly in a definite plane; if deflected therefrom they oppose resistance and are ready to do work in returning thereto. Of kindred to the kinetic theory of elasticity is the explanation of heat as a distinct and ceaseless molecular motion on which the dimensions of masses depend. It has long seemed to me that every case of “potential” energy, as that of a spring bent or coiled, may in like manner embody actual though impalpable and invisible motion. I presented this view in the Popular Science Monthly, December, 1876.