( 569 ) 
On the other hand »'= v; hence, by (I) and (ID), 
b’—- —d and Da Hi 
Now let us put in the field, produced by the pair of ions, a 
similar pair with charges e and e= —e, and moving with the 
common velocity ». Then, by (10)—(13), 
B | 
The total force on the positive particle will be 
a) 
a 
and that on the negative ion 
An (ree) 
a 
These forces being equal and having the same direction, there is 
no force tending to separate the two ions, as would be the case in 
an electric field. Nevertheless, the pair is acted on by a resultant 
force 
2 ky (1 a 2 ): 
If now / be somewhat larger than @, the factor 2 (1 — ©) wit 
a 
have a certain negative value — «, and our result may be expressed 
as follows: 
If we wish to determine the action between two ponderable bo- 
dies, we may first consider the forces existing between the positive 
ions in the one and the positive ions in the other. We then have 
to reverse the direction of these forces, and to multiply them by the 
factor «. Of course, we are led in this way to Newron’s law of 
gravitation. 
The assumption that all ponderable matter is composed of posi- 
tive and negative ions is no essentiaì part of the above theory. We 
might have confined ourselves to the supposition that the state of 
the aether which is the cause of gravitation is propagated in a 
similar way as that which exists in the electromagnetic field. 
41 
Proceedings Royal Acad, Amsterdam. Vol. IL. 
