An instructive experiment may be made: First, finely pulverize indigo, charcoal, or carmine, and then mix either of them with water, and place under the microscope, when an incessant movement of the small granular particles will become apparent; and the smaller the particles, the more rapid and uniform will be their movements. These movements are chiefly of a vibratory kind; and it is when the particles are minutely divided, so as to approach the limits of microscopic range, that this vibratory motion, together with an irregular axial rotation, approaches a degree of perfection that is beautiful as well as suggestive. This experiment is well calculated to assist us in forming a mental conception of the magnitudes and the motions of those atoms and molecules which have for their realm the regions below and beyond the immeasurably small.
As to the shape and internal structure of atoms, there is no definite knowledge; but Helmholtz's studies of certain equations in hydro-kinetics, several years ago, gave rise to the idea that vortex-motion in a frictionless medium would exist forever—an assumption which is purely hypothetical; but since the proposition has been enlarged upon by Sir William Thomson—who conjectures that the atoms might be filaments or rings endowed with a vortex-motion—the subject assumes a shape better calculated to form the basis of a scientific theory. To be sure, mathematical formulas might show that the behavior of a vortex-filament in a non-resisting medium would answer to that ascribed to atoms—indestructible and unalterable through all time; still, at the same time, the means at hand for its complete mathematical verification are not adequate to place the subject beyond the regions of theory. Prof. Tait, in a review of this subject in his "Recent Advances of the Physical Sciences," remarks that, "with a little further development, it may be said to have passed its first trial, and, being admitted as a possibility, may be left to time and the mathematicians to settle whether it will really account for everything experimentally found."
Small as these atoms are, we are not permitted to stop here, but remember that there is a finer medium environing them all, embracing possibly a complexity of internal structure sufficient to baffle human investigation for all time. This cosmic or luminiferous ether is supposed to fill all space, intermolecular and interstellar, and to be the medium in which the atoms and molecules move like motes in the sunbeam.
Atoms and molecules may vibrate to and fro, or may execute various oscillations about each other, with a moderate velocity, or perform their motions with a rapidity beyond conception; and be the intensity of the vibrations ever so great or ever so small, these same vibrations determine the amplitude of the ethereal waves—those waves of greatest length giving rise to all the phenomena of radiant heat, while shorter ones constitute light in all its luminous and chromatic effects; as also
