Existence of the Luminiferous ^Etlier. 485 



(d) The molecular refracting-power of the acids of the fatty 

 series is 7'6n+6, where n is the number of atoms of carbon 

 in the acid. But if the increase in molecular refracting- 

 power for H 2 is equal to 2' 6, that for H will equal 1*3. Thus 

 we get a number which gives us the atomic refractiug-power of 

 one atom of H in these compounds. In the same way the 

 atomic refracting-power of carbon is found to be 5, and that 

 of oxygen 3. Knowing these numbers, the molecular refract- 

 ing-power of a body of known composition can be calculated. 

 For example, take ethylic acetate, C 4 H 8 2 : by calculation we 



have 4x5 + 8x1-3 + 2x3 = 36-4 for the value of ^^M. 



a 



By actual experiment d is found to be -8977, n — 1*3715, and 

 M = 88; thus again giving 36*4. These results have been 

 obtained from the researches of Gladstone and Dale and 

 Landolt. Recently the subject has been taken up with 

 marked success by Briihl (A?inalen, vols. cc. and cciii., Berichte, 

 vol. xiii.) He has corrected the values given above for the 

 atomic refracting-powers of carbon, hydrogen, and oxygen, and 

 has determined others. (Gladstone has also given a very 

 complete list.) Brtihl has deduced the following conclu- 

 sions : — 



(1) The atomic refraction of monad elements is constant. 



(2) When an organic body loses two atoms of H, forming 

 a compound in which two of the carbon atoms are linked 

 together by a double affinity, the specific gravity increases by 

 •04, the coefficient of refraction by '02; and the dispersion is 

 also greater. 



(3) Variations in atomic refraction occur in the case of 

 multivalent elements. 



Now here we have a mass of facts deduced from a large 

 number of experiments plainly showing the very close re- 

 lation that exists between the atomic structure of pure che- 

 mical compounds and the transmission of light through them. 

 The relationship is in fact so close that the deduction even 

 forces itself upon us, that the molecules of bodies are themselves 

 the vehicles of light-motion. Assuming the existence of the 

 luminiferous aether between the molecules of bodies, and also as- 

 suming that the wave-motion is transmitted by the aether, how 

 are these results explained ? Examined in whatever way we 

 please, they will still remain inexplicable. Let us consider (as 

 an example of the whole) the first of the rules, viz. isomeric and 

 metameric bodies have the same refractive power. As iso- 

 meric and metameric bodies have the same percentage compo- 

 sition and the same number of atoms of each element, if we 

 consider the molecules of bodies themselves concerned in the 



