ELISHA MITCHELL SCIENTIFIC SOCIETY. 99 



The general acceptation of the Law of Periodicity has been 

 another potent factor in drawing attention to the need for care- 

 ful revision, and in many cases re-determination of the atomic 

 weights. Those who have undertaken this revision have met 

 with many serious obstacles which are still very far from beinLi 

 overcome. This, I think, will be seen as we proceed in the dis- 

 cussion of the results obtained. 



THE UNIT OR BASIS. 



The first essential is the adoption of a unit of calculation or 

 basis, and this has proved one of the great obstacles in the way 

 of uniformity. Two elements suggest themselves as bases for 

 these calculations — hydrogen and oxygen. For fifty years or 

 more the strife has raged as to which of these should be adopted. 

 Hydrogen has been practically adopted and used, but the oppo- 

 sition to it has only slumbered at times and seems rising again 

 in the past few years. Dalton and Gmelin were the advocates 

 of the hydrogen unit in early days and Wollaston and Berzelius 

 advocated oxygen. Among the late revisers and recalculators 

 Becker* refers all the atomic weights to oxygen —16. Clarkef 

 gives tables calculated either for oxygen=16 or hydrogen=l. 

 Sebelien."!: uses the units, hydrogen=l or oxygen=100, as also 

 do Meyer and Seubert§. Ostwald^f uses bydrogen=l, giving to 

 oxygen the value 16. Van der Plaats|| has selected oxygeu=K) 

 as the basis for his recalculation. 



There is a decided predominance of authority in favor of 

 oxygen as the standard and of giving it the value 16, though 

 -nine would make it appear that this is the same thing as adopt- 

 ing hydrogen=l. 



^Constants of Nature, Part IV, Smithsonian Institution, L880. 

 fConstants of Nature, Pari V, Smithsonian Institution, 18s7. 

 JBeitrii ^e zur (icsdiichte der Atoragewichte, 1884. 

 MM'e Atomgewichte der Elemente, 1883. 

 ^[Lehrbueh der Allgemeinen Cheruie, 1885. 

 | Annales de Chiruie et de Physique (6 serie) 7 April, 1886. 



