

The Crémieu-Pender Discovery. 405 
to the square of an electric quantity associated with the 
molecule. Thus rigidity is proportional to the square of an 
electric quantity. Now our law for the dielectric capacity 
of an atom means that the square of K,/y for an atom when 
multiplied by the volume of the atom is the same for all. It 
seems, then, as though a certain stock of electric energy 
associated with the electrons in an atom were the same for all 
atoms. The law for K,, then, seems to be of a similar nature 
to that of Dulong and Petit and of the fundamental law of 
molecular physics which makes the kinetic energy of transla- 
tion of all molecules at a given temperature the same. 
But to return from speculation to the immediate bearings 
of the formula K,B?/v=constant ; we find that in (16) “it 
makes the ionic velocity of an atom directly proportional to 
the sixth root of the volume of the atom—that is to say, to 
the square root of its radius. This brings out neatly the old 
paradox about ionic velocities. Hither to it has been assumed 
that the ionic velocities have all been measured with the same 
driving force for all ions. The result that a large ion like 
that of K travels faster than a small one like that of Li under 
the same driving force in a resisting medium is, indeed, 
puzzling until, in taking account of the dielectric capacity of 
the atom, we see that the driving forces assumed equal are 
in reality not so at all. 
Melbourne, December 1903. 




L. The Crémieu-Pender Discovery. 
By WituiaAM SUTHERLAND * 
ib the experiments carried out by the happy collaboration 
of Messrs. Crémieu and Pender (Phil. Mag. Oct. 1903) 
practically the whole of the difficulty in reconciling the 
apparently contradictory results obtained by Rowland and 
his pupils and Réntgen, Himstedt, and others on the one 
hand, and by Crémieu on the other, concerning the magnetic 
effects of electric convection was traced to the one fact that 
Crémieu covered his metallic electrified surfaces with solid 
dielectric. The solid dielectric rotating with the revolving 
charged metallic disk reduces the magnetic effect con- 
siderably, so as in some experiments to make it appear to 
vanish. The combined experiments have brought into pro- 
minence a fundamental property of dielectrics. Now exactly 
the same property made itself apparent in my theoretical 
* Communicated by the Author. 
