196 



Mr. D. Gill. On the Presence of Oyxgen 



Since, as we have shown, the charge on an ion produced by Rontgen 

 rays is equal to the charge on a hydrogen ion in a liquid electrolyte, 

 this latter charge is also 6 x 10~ 10 electrostatic unit. 



Although the value of N<? for hydrogen is 25 per cent, less than its 

 value for other gases, we are justified in including hydrogen in the 

 above general conclusion, as we should expect the value of u for hydro- 

 gen to be too small. Professor Rutherford makes no mention of 

 having corrected for the presence of air in his apparatus, or of having 

 used perfectly dry hydrogen. If we take the mean value of k for 

 moist hydrogen, we obtain N<?h = 1"15 x 10 10 . 



In order to prove that the charge on the positive ion is equal to the 

 charge on the negative ion, the ratio of the coefficients of diffusion 

 must be shown to be equal to the ratio of the velocities. Professor 

 Zeleny* has shown that the negative ions travel faster under an elec- 

 tromotive force than the positive ions, the ratios of the velocities being 

 1*24 for air and oxygen, 1*15 for hydrogen, and 1*0 for carbonic acid. 



The experiments on diffusion show that the ratio of the velocities 

 would be larger in dry than in moist gases ; but as this point has not 

 yet been examined by Professor Zeleny, we cannot expect a very close 

 agreement between the ratios which he gives for the velocities and the 

 ratios of the coefficients of diffusion. 



We are led to conclude that the charges on the positive and nega- 

 tive ions are equal from another point of view. It has been proved 

 that the mean charge is the same as the charge on an ion of hydrogen 

 in a liquid electrolyte. If the charges differed, one of them would be 

 less than the charge on the hydrogen ion, whereas experiments on 

 electrolysis show that all ionic charges are either equal to the charge 

 on the hydrogen ion or an exact multiple of it. 



" On the Presence of Oxygen in the Atmospheres of certain Fixed 

 Stars." By David Gill, C.B., F.R.S., &c, Her Majesty's 

 Astronomer at the Cape of Good Hope. Received April 14, — ^ 

 Read April 27, 1899. 



(Plate 8.) 



In a paper read before the Society on April 8, 1897, and in a sub- 

 sequent paper,! Mr. Frank McClean draws attention to the group- 

 ing of lines other than those of helium and hydrogen in the spectra 

 of p Scorpii, p Canis Majoris, p Centauri and p Crucis, suggesting 

 that the close correspondence between the grouping of these extra 

 lines and the known lines of oxygen, points to the probable presence 

 of that gas in th.3 atmospheres of these stars. 



* J. Zeleny, ' Phil. Mag.,' July, 1898. 



t ' Roy. Soc. Proc.,' vol. 42, JNo. 386, p. 418. 



