in Magnetism and Electricity. 93 



ties of the electrohelices 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 imme- 

 diately to the attractive force of the small electromaguet placed 

 beneath it, so long as the electricity from the machine was trans- 

 mitted through the helices of the large electromagnet ; but when 

 contact with the machine and the electrohelices was broken, it 

 was observed that the submagnet was instantly withdrawn from 

 the poles of its electromagnet 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 electromagnet 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 electromagnet 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 electromagnet (67, 68) excited by the same mag- 

 neto-electric machine (18), the electromagnetic balance did not 

 respond to the attractive force until an interval of 15 seconds 

 had elapsed. 



45. But if the retardation of the current, as indicated by the 

 balance when placed in the middle of the circuit, had been the 

 effect of an accumulation of static electricity in the electrohelices, 

 it would also have been instantly attended by a rush of the full 

 current of electricity into the helices at the beginning of the 

 circuit, such as was observed in the before- mentioned experi- 

 ments made by Faraday (40). On making the experiment, how- 

 ever, this was not found to be the case ; for when the balance 

 was removed from the middle and placed at the beginning of 

 the electromagnetic circuit, the wires being again joined up so 

 as to form a continuous helix as before (33), it was still found 

 that 1*5 second, and with the large electromagnet (67, 68) 15 

 seconds, elapsed before the electricity acquired sufficient power 

 to bring down the submagnet of the balance. 



46. When the large electromagnet (67, 68) was excited by 

 the electricity from a larger and more powerful machine (63) 

 driven at a velocity of 2000 revolutions (equivalent to 4000 

 waves) per minute, instead of that from the small magneto-electric 

 machine, which produced 6000 waves per minute, an interval of 

 only four seconds elapsed before the balance responded to the 

 attractive force of its electromagnet. 



