48 



Messrs. Boys, Briscoe, and Watson on the 



Fig. 2. 

 \ full size. 



It follows from this that, if the oscillations be forced and 

 made too slow, the accumulation of charge on the ends will be 

 greater for a given maximum current than it would be if the 

 period were natural, and therefore the repulsion should over- 

 power the attraction. In the same way, with too rapid vibra- 

 tions the attraction should overbalance the repulsion. Also 

 since, if the wires are not close together, the electrostatic 

 repulsion will have fallen away in a higher ratio than the 

 electrodynamic attraction, it would appear that resonators 

 which balance when close should attract one another when at 

 a distance, or that resonators subject to forced oscillations 

 which repel when near might attract when at a distance. 



Prof. Fitzgerald, when the above theory of the mutual 

 action of resonators was put to him, at once suggested that if 

 the molecules of a body were subject to electrical oscillations 

 it would be possible to imagine a physical cause 

 for their supposed attraction when far, and 

 repulsion when close. 



In order to test the matter experimentally, 

 the wires were made of a cranked form, as 

 shown in fig. 2, so that the ends were on one 

 side of a vertical axis (dotted), and the middle 

 part on the other side. Then, if one is held 

 close to the other, and if the second one is free 

 to turn about the vertical axis, the attraction of 

 the centre and the repulsion of the ends should 

 conspire to produce rotation in the same 

 direction*. 



The first experiment was made with a pair 

 of copper wires each one foot long, bent so 

 that the end parts were each 2\ inches, the 

 middle part 5 inches, and the horizontal part 

 1 inch. This was suspended in a glass jar by 

 a quartz fibre, so that the vertical axis of 

 rotation was halfway between the ends and 

 the middle portion. An ordinary galvanometer- 



* It may be worth mentioning that the invention of this method was 

 made in a particularly vivid dream, in which I found myself at the black- 

 board in the physical lecture-room, explaining that if the two wires were 

 close together, the currents in each would be going up and down together, 

 and so would attract one another, and that in order to make this attrac- 

 tion evident, the wire should be suspended near the axis of rotation, for 

 the reason that where quartz -fibres can be employed there is a greater 

 gain owing to the reduction of moment of inertia than loss by reduc- 

 tion of statical moment. I did not in the dream see that the charges 

 should repel, or the necessity for the cranked form of wire. I may say 

 that this was after Mr. Qregory had described his instrument, but the 

 idea of looking for mutual attraction between a pair of resonators had 

 not before ocaurred to me. — C. V. B. 



