364 Mr. S. Tolver Preston on Method 



a possible insight that this constitution of the aether might 

 afford into the transverse vibrations of light, and the effects of 

 gravity (under Le Sage's sheltering principle), by admitting 

 that the atoms have an adequately long mean path — I must 

 refer to a previous article * in ' Nature ' vol. xxi. page 256, 

 and also Phil. Mag. Sept. & Nov. 1877. 



At least it appears to the writer that to explain the observed 

 absence of resistance to the passage of bodies through the 

 aether is very important. It is difficult to imagine what is 

 supposed to take place in these " statical " theories, where the 

 aether is supposed to consist of material particles in fixed posi- 

 tions and assumed to be acting on each other by " forces " at 

 a distance, or the constitution of the aether is regarded as 

 resembling that of a " solid." What becomes of the delicate 

 structure of particles and " forces " in the " solid " with (say) 

 the immense mass of the earth flying through the "solid" 

 at about 18 miles per second ? Can even the fertile resources 

 of these plastic theories, when taxed to their utmost extent, 

 be of avail here ? The objection is not the less cogent because 

 elementary. 



There would seem to be sometimes a certain looseness of 

 reasoning or carelessness in regard to the treatment of the 

 aether, that would be considered out of place in ordinary 

 mechanical problems. Sir John Herschel, whose expositions 

 are known in general to have been distinguished for their 

 clearness and lucidity, seems to have made an exception in the 

 case of the aether. In referring to the speculation as to the 

 aether being a " solid," he (' Popular Lectures,' page 285) 

 defines the solidity of the aether in the sense, that none of its 

 elementary molecules are to be supposed capable of interchanging 

 places t, or of bodily transfer to any measurable distance from 

 their own special and assigned localities in the universe." 

 What (one might ask) becomes of the molecules of aether in- 

 capable " of bodily transfer from their own assigned localities," 

 with a planet careering through them, or the solar system in 

 its proper motion of several miles per second through space ? 



The vague and loose reasoning occasionally applied to the 

 aether, may perhaps be partly accounted for from the feeling of 

 utter hopelessness as to making any advance when all efforts 

 are paralyzed by the boundless labyrinth of speculation involved 

 in the assumption of "force." Can it be seriously believed 



* The proposed mode of accounting for the transverse -vibrations of 

 light, given in the article ir. ' Nature/ was based on a suggestion or hint 

 thrown out by Prof. Clerk Maxwell, under subject " Ether" (Encyc. Brit. 

 new edition). 



t The italics are Sir John Herschel's. 



