192 F W. Very— A Cosmic Cycle. 



The relative abundance of the elements remains a puzzle on 

 any hypothesis. Oxygen and silicon prevail in the outer part 

 of the earth, hydrogen and calcium on the outside of the sun ; 

 but the earth's mean density requires that a large part of its 

 interior shall consist of something not far from the density of 

 iron ; and the prevalence of this substance in meteorites, as 

 well as its relative abundance in. the sun, implied by the breadth 

 and intensity of many of the iron lines in the solar spectrum, 

 suggests that iron may turn out to be one of the most abundant 

 elements in nature. If so, it may be something more than a 

 coincidence that iron is a highly magnetic element, and that 

 magnetism has given us a means of changing, if only tempo- 

 rarily, such a persistent elemental property as the wave-length 

 of spectral lines. 



Until someone shall suggest criteria for the stability of 

 different possible forms of vortex-motion, I do not see how we 

 can go farther in this direction. 



Properties of the Luminiferous Ether. 

 I shall not enter upon questions relating to the constitution 

 of the unmodified ether previous to the inauguration of the 

 ethereal movement constituting atoms : whether the ether is 

 composed of vortex-filaments giving a fibrous structure and a 

 quasi-elasticity ; whether the rectilinear motion of an atom 

 through the ether is to be likened to the propagation of a wave 

 in water, where the wave advances, but not the particles of the 

 medium ; or whether, like an aerial vortex-ring, the same 

 ethereal particles continue perpetually in an individual atom ; 

 whether, indeed, the ether can be said to have "particles'' in 

 this sense ; whether the intrinsic motion of the ether is circu- 

 latory, and all change in the ether is a compounding or a propa- 

 gation of rotational energy ; etc. But the question of the 

 relation of the ether to gravitation is of such importance that 

 it must be considered. In the ninth edition of the Encyclo- 

 paedia Britannica, Maxwell has given a computation of the 

 density of the ether, referred to water, getting 9*36 X 10" 19 . 

 A numerical mistake is nearly balanced by the use of Pouillet's 

 value of the solar constant. Correcting the error and substi- 

 tuting three small calories per minute on each normal square 

 centimeter (0*05 radim) for the solar constant, the density of 

 the ether comes out 9* L7 X 10" ' ° . The whole computation rests 

 on the assumption that the amplitude of an ether-wave from 

 the sun, near the sun's surface, is yi^ of the average wave- 

 length. There is not the slightest evidence that there is any 

 such relation between ethereal amplitude and wave-length ; 

 and the array of figures has not even qualitative value, since 

 the method involves some unsafe tacit assumptions. 



