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ME. II. WILDE’S EXPERIMENTAL RESEARCHES 
it was found that neither the small electro-magnet (22, 23) nor the large electro-magnet 
(33) would sustain even a weight of 1 lb. 
40. It was at first thought that the great difference observed between the sustaining- 
power of the electro-magnet and that of the permanent magnets which excited it, might 
be due to the helices surrounding the electro-magnet absorbing or retaining the electricity 
transmitted through them in a static condition, in the manner observed in insulated sub- 
marine and subterranean telegraph wires ; an investigation of which phenomenon, as it 
was manifested in gutta-percha-covered wires submerged in a canal, and in similar wires 
laid underground between London and Manchester, was made by Faraday in 1853*. 
41. For the purpose of ascertaining whether this view of the subject was correct, a 
Very small and delicate electro-magnetic balance was constructed, similar in principle to 
the one shown in fig. 8. The small electro-magnet, fixed beneath one end of the balance, 
was coiled with a strand of insulated copper wires 6 feet in length and 0T5 of an inch 
in diameter. The submagnet was prevented from coming into contact with the poles 
of the electro-magnet by means of regulating-screws. Other regulating-screws limited 
the movements of the balance in the opposite direction; ,and the distance of the sub- 
magnet from the electro-magnet could also be adjusted, by means of the same regulating- 
screws, to suit the different quantities of electricity transmitted through the electro- 
helices. 
42. This electro-magnetic balance was placed in the middle of the circuit of the 
electro-magnet (33), i. e. at the point where the two electro-helices were joined together. 
The poles of the magneto-electric machine were then connected with the free extre- 
mities of the electro-helices for a few seconds ; and after the spark from the commutator 
had disappeared, the submagnet was so counterpoised, by means of small weights, as to 
respond immediately to the attractive force of the small electro-magnet placed beneath 
it, so long as the electricity from the machine was transmitted through the helices of the 
large electro-magnet ; but when contact with the machine and the electro-helices was 
broken, it was observed that the submagnet was instantly withdrawn from the poles of 
its electro-magnet by the weights placed in the scale-pan at the, opposite end of the 
balance. 
43. The apparatus being thus arranged, it would follow that if the charge in the wire 
surrounding the electro-magnet were identical with that which is observed in insulated 
submarine-telegraph cables, a certain interval of time would elapse, after contact with 
the magneto-electric machine had been made, before the balance in the middle of the 
circuit would respond to the attractive force of the small electro-magnet placed beneath 
it. On making the experiment it was found that when contact was made with the 
machine, 1*5 second elapsed before the balance responded to the attractive force. 
44. When placed in the middle of the circuit of a larger and more powerful electro- 
magnet (67, 68), excited by the same magneto-electric machine (18), the electro-magnetic 
balance did not respond to the attractive force until an interval of 15 seconds had elapsed. 
* Proceedings of the Royal Institution, Jan. 20th, 1854. 
