ÆTHER BY DeVOLSON WOOD, C. E., M.A. Reprinted from the "Philosophical Magazine" with Additions. NEW YORK: 1886. THE LUMINIFEROUS ÆTHER. Two properties of the luminiferous æther appear to be known and measurable with a high degree of accuracy. One is its ability to transmit light at the rate of 186,300 miles per second,* and the other its ability to transmit from the sun to the earth a definite amount of heat energy. In regard to the latter, Herschel found, from a series of experiments, that the direct heat of the sun, received on a body at the earth capable of absorbing and retaining it, is competent to melt an inch in thickness of ice every two hours and thirteen minutes. This is equivalent to nearly 71 foot-pounds of energy per second. *Professor Michelson found the velocity of light to be 289,740 meters per second in air, and 299,828 meters in a vacuum, giving an index of refraction of 1,000,265 "Journal of Arts and Science," 1879, vol. xviii., p. 390. In 1838 M. Pouillet found that the heat energy transmitted from the sun to the earth would, if none were absorbed by our atmosphere, raise 1.76 grammes of water 1° C. in one minute on each square centimeter of the earth normally exposed to the rays of the sun.❤ This is equivalent to 83.5 foot pounds of energy per second, and is the value used by Sir William Thomson in determining the probable density of the æther.† Later determinations of the value of the solar constant by MM. Soret, Crova, and Violle have made it as high as 2.2 to 2.5 calories. But the most recent, as well as the most reliable, determination is by Professor S. P. Langley, who brought to his service the most refined apparatus yet used for this purpose, and secured his data under favorable conditions; from which the value is found to be 2.8 calories with some uncertainty still remaining in regard to the first figure *Comptes Rendus, 1838, tom. vii. pp. 24-26. + "Trans. Roy. Soc. of Edinburgh," vol. xxi. part 1. + Am. Journ. of Arts and Science, March, 1883, p. 195. Also Comptes Rendus. of the decimal. We will consider it as exactly 2.8 in this analysis, according to which, there being 7,000 grains in a pound and 15.432 grains in a gramme, we have for the equivalent energy per second for each square foot of surface normally exposed to the sun's rays, which value we will use. Beyond these facts, no progress can be made without an assumption. Computations have been made of the density, and also of the elasticity,X of the æther founded on the most arbitrary, and in some cases the most extravagant, hypotheses. Thus, Herschel estimated the stress (elasticity) to exceed 17x10° = (17,000,000,000) pounds * and this high authority has doubtless caused it to be widely accepted as ap "Familiar Lectures," p. 282 |