504 • Dr. Gr. J. Stoney on the 



anode drop is, as at the cathode, to slightly reduce it, but this 

 is greatly overweighed by the indirect effect produced by the 

 increased potential gradient in the gas. 



The effect of a magnet on the cathode drop is probably to 

 be ascribed to a factor which has been ignored in the fore- 

 going considerations, namely, to the electromagnetic inertia 

 of the ions, in that the magnetic field in constraining the 

 oscillations of the ions facilitates their discharge. 



Physical Laboratory, 

 University of Nebraska, Lincoln. 



LTV. Oik the Law of Atom ic J \ r e ig It t a . 

 u i forecast. 



To the Editors of the Philosophical Magazine. 

 Gentlemen, 



THE letter on the Law of Atomic Weights which you 

 were so good as to publish last month, was necessarily 

 limited to a description of results arrived at several years 

 ago, along with the insertion upon a diagram which had been 

 constructed in 1888, of a series of elements since discovered. 



To those earlier results I request you to allow me to add a 

 forecast, which I desire to put forward in the hope that the 

 appropriate laboratory tests may be applied to it. 



In the diagram reproduced in Plate IV. of last month's 

 magazine, shaded prominences were introduced to point out. 

 the elements of greatest atomic volume in the solid state, and 

 •shaded sectors to indicate those of least atomic volume. In 

 1888, when that diagram was designed, it was the elements 

 bn sesqui-radius 1 that were preeminent in atomic volume 

 amongst the elements then known. But now that sesqui- 

 radius 16 is occupied, the diagram suggests, and appears 

 to suggest with considerable emphasis, if we recognize 

 that the physical properties of the elements are controlled 

 by general laws, that the column of shaded prominences 

 on sesqui-radius 1 should be shifted to sesqui-radius 16. 

 This would mean that it is the new elements on sesqui-radius 

 16, and not the elements on sesqui-radius 1, which possess 

 the greatest atomic volume in the solid state. 



To ascertain by experiment whether this is so in the case 

 of helium would probably overtask the most refined methods 

 of low-temperature research yet known. But it ought to be 

 possible to determine the specific gravity in the solid state of 

 xenon, krypton, argon, and neon ; and if the forecast is found 

 to be correct in regard to these four elements, its fulfilment will 



