The new chemistry / by Josiah P. Cooke.

  • Cooke, Josiah P., Jr. (Josiah Parsons), 1827-1894.
Date:
1874
Catalogue details

Licence: Public Domain Mark

Credit: The new chemistry / by Josiah P. Cooke. Source: Wellcome Collection.

    28/336 (page 22)
    is perfectly true that we liave no absolute knowledge of the nature of a beam of light. We have a very plausible theory that the phenomena of light are the effects of waves transmitted through a highly-elastic medimn we call ether, and that, in the case of our plate of glass, the motion is transmitted through the ether, which fills the interstices between the molecules of this transparent solid; but we have no right to assume this theory in our present discussion. Indeed, I cannot agree with those who regard the wave-theory of light as an established principle of science. That it is a theory of the very highest value I freely admit, and that it has been able to j)redict the phases of imknown phenomena, which experiment has subsequently brought to light, is a well-known fact. All this is true ; but then, on the other side, the theory requires a combination of qualities in the ether of space, which I find it difficult to believe are actually realized. For instance, the rapidity with which wave-motion is transmitted depends, other things being equal, on the elasticity of the medium. Assuming that two media have the same density, their elasticities are proportional to the squares of the velocities with which a wave trav- els. The velocity of the sound-wave in air is about 1,100 feet a second or -I- of a mile, that of the light- wave about 192,000 miles a second, or about one million times greater; and, if we take into account certain causes, which, though they tend to increase the velocity of sound, can have no effect on the luminiferous ether, the difference would be even greater than this. Now, were the density of the ether as great as that of the atmosphere (say -J of a grain to the cubic inch), its elasticity or jjower of resisting pressure would be a million square, or a million million times that of the