428 Lord Bayleigh. [Mar. 7, 



December 24, 1888 15'93 



January 3, 1889 15'98 



21, ' 15-98 



February 2, 15'93 



13, 15-92 



Mean 15'95 



This number represents the atomic ratio of oxygen and hydrogen 

 as deduced immediately from the weighings with allowance for the 

 unburnt residue. It is subject to the correction for buoyancy 

 rendered necessary by the shrinkage of the external volume of the 

 globes when internally exhausted, as explained in my former commu- 

 nication.* In these experiments, the globe which contained the 

 hydrogen was the same (14) as that employed for the density deter- 

 minations. The necessary correction is thus four parts in a thousand, 

 reducing the final number for the atomic weight of oxygen to 



15-89, 



somewhat lower than that which I formerly obtained (15*91) by the 

 use of Mr. Scott's value of the volume ratio. It may be convenient 

 to recall that the corresponding number obtained by Cooke and 

 Richards (corrected for shrinkage) is 15*87, while that of Keiser is 

 15-95. 



In the present incomplete state of the investigation, I do not wish 

 to lay much stress upon the above number, more especially as the 

 agreement of the several results is not so good as it should be. 

 The principal source of error, of a non-chemical character, is in the 

 estimation of the weight of the hydrogen. Although this part of the 

 work cannot be conducted under quite such favourable conditions as 

 in the case of a density determination, the error in the difference of 

 the two weighings should not exceed 0'0002 gram. The whole weight 

 of the hydrogen used is about O'l gram ;f so that the error should 

 not exceed three in the last figure of the final number. It is thus 

 scarcely possible to explain the variations among the five numbers as 

 due merely to errors of the weighings. 



* The necessity of this correction was recognised at an early stage, and, if I 

 remember rightly, was one of the reasons which led me to think that a redetermina- 

 tion of the density of hydrogen was desirable. In the meantime, however, the 

 question was discussed by Agamennone (' Atti (Kendiconti) d. E. Accad. dei Lincei,' 

 1885), and some notice of his work reached me. When writing my paper last year 

 I could not recall the circumstances ; but since the matter has attracted attention I 

 have made inquiry, and take this opportunity of pointing out that the credit of first 

 publication is due to Agamennone. 



f It was usual to take for combustion from two-thirds to three-fourths of the 

 contents of the globe. 



