218 Mr. W. Ellis on the Influence of the ' 



heat, it would be at once the surest proof that the molecule of 

 these two bodies consists of only a single atom, and that the 

 molecules of most of the other undecomposed bodies consist of 

 two atoms and not of a multiple of two atoms, and that those of 

 phosphorus and arsenic consist of four atoms. 



In the foregoing pages it has been shown that for the per- 

 fectly gaseous state the heat of expansion bears a simple constant 

 ratio to the heat of molecular motion, — and also, on the basis of 

 Pegnault's experimental results, that the heat of atomic motion 

 bears a simple ratio to the two already-mentioned parts of the 

 specific heat, the heat of atomic motion being found proportional to 

 the number of atoms in a molecule. Thus the ratio of the heat 

 of expansion to the heat of molecular motion and to that of 

 atomic motion has been found to be — 2 : 3 : n, and for the spe- 

 cific heat the general expression ry T =2a + 3a-r na=(n + 5)a has 

 been obtained ; and this, when (from the results of Regnault's 

 experiments) the value 0*034 has been found for a, reduces 

 itself to the numerical expression 7'= (71 + 5)0*034. Since the 

 agreement between the numbers thus calculated and those de- 

 duced from experiment, is in general greater the nearer a gas 

 approaches to the presupposed state of a perfect gas, and since 

 also the numerical values of other kinds deduced from the equa- 

 tions that have been established agree with the results of expe- 

 riment, the simple conclusions to which the foregoing conside- 

 rations lead, and the consequences connected with them, appear 

 to be sufficiently established. 



Giessen, December 1866. 



XXVIII. Some further Remarks on the Influence of the Full 

 Moon on Cloud. By William Ellis, F.R.A.S. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 "Vl^ILL you allow me space briefly to reply to the remarks 

 y* made by Mr. J. Park Harrison on my paper on the In- 

 fluence of the Full Moon on Cloud ? What I wished to show, 

 in the particular case which I investigated, was that no great 

 effect exists, none that we can easily perceive. It is to be re- 

 membered that the language of Herschel and Arago is very 

 strong on the point. Herschel, in his ' Familiar Lectures,'' speaks 

 confidently of the tendency of the moon "to clear the sky of 

 cloud, and to produce, not only a serene, but a calm night, when 

 so near the full as to appear round to the eye." And Arago 

 says, " La lune mange les images." This does not indicate a 



