ADVERTISEMENT. 



The present memoir is the result of a series of investigations by Professor 

 Moi'ley, which have been aided to some extent during the last two years by the 

 Smithsonian Institution. 



The atomic weight of oxygen may be called the base line upon which practi- 

 cally oui' entii-e system of atomic weights depends, and a small error in its measure- 

 ment becomes large by multiplication in the higher parts of the atomic weight 

 scale. Hence its accurate determination is of fundamental importance. 



In his investigation, Professor Morley has studied the problem by two 

 methods. 



1st. By the synthesis of water, in which he, for the first time, has achieved 

 completeness by actually weighing the hydrogen, the oxygen, and the water formed, 

 whei-eas all his predecessors took one or another of these factors by dift'ei'ence. 



2d. By the density ratio between oxygen and hydrogen. In this method he 

 has weighed the gases of greater purity and in larger quantity than hitherto, and 

 he has in some instances operated without the intervention of stopcocks, and there- 

 fore with no possibility of ei'ror due to leakage. He has also, as a cori-ection to 

 the density ratio, redetermined the composition of water by volume. 



By both methods he reaches the same result : 



O = 15-879. with variation in the fourth decimal place as between the two. 



In accordance with the rule adopted by the Smithsonian Institution, the work 

 has been submitted for examination to a committee consisting of Professor F. AV. 

 Clarke and Doctor Cai-1 Barns, and having been i-ecommended for publication 

 it is herewith presented in the series of Contributions to Knowledge. 



SMiTHSONiAisr Institution, 



WasJdngton, July, 1895. 



S. P. Langley, 



Secretary. 



