Mr. W. Sturgeon's Electro-magtietica! Experiments. 267 



to the directive exertion of the forces of the differently excited 

 wires or machines, yet it is not impossible that some may 

 still doubt of the sufficiency of those experiments to determine 

 the apparently anomalous phenomena : owing, perhaps they 

 may say, to the difference of the construction of the apparatus 

 employed for exhibiting them. I am persuaded, however, 

 that the following mode of making the experiments will, in 

 all probability, be sufficiently decisive to convince the most 

 sceptical on this point. 



Suspend the semi-circular copper arc, with its zinc diame- 

 ter, as described in my former paper (the extremities of the 

 metals need not be soldered but twisted together). Wrap one 

 of those joinings of the metals loosely with a piece of tow or 

 unspun cotton. Dip this part of the machine into dilute nitric 

 acid (observe to counterpoise at the other end) ; present the 

 north pole of a magnet to the same arm, and it will be pro- 

 jected to the right. 



Take off the cotton, wash and dry the machine, and suspend 

 it as before. Apply the lamp now instead of the acid, and the 

 magnet as in the former experiment; that arm of the ap- 

 paratus will be now propelled to the left. 



I have merely pointed out this method of making the ex- 

 periments, as the most likely to be understood in comparing 

 the phaenomena ; but that described with the galvanoscope, for 

 making the chemico experiment, is by far the most efficient 

 and eligible. 



The results obtained from the mode of comparing chemico 

 and thermo phenomena, could hardly fail to suggest the idea, 

 that chemico-excited wires would have their electrical tension 

 increased by thermo application at the opposite extremity. 

 And in order to try the suggestion by the test of experiment, 

 I had recourse to the above-described simple apparatus. I 

 twisted the copper wire a good length round the extremities 

 of the zinc, so that as great a metallic surface as possi- 

 ble might be exposed to the action of the acid. After dipping 

 the extremity wrapped with tow into the acid, I suspended 

 the machine in the galvanoscope. On presenting the north 

 pole of the magnet to the arm ascending from the chemico 

 extremity, the latter was deflected to the right about 80°. 

 From that it returned to nearly 20° : thence propelled again 

 to nearly the same distance as before ; and so vibrating several 

 times from about 15° to 60°, when I changed the pole of the 

 magnet. It was now deflected in a contrary direction (left) to 

 about 70° : from thence it returned as before by the silk en- 

 deavouring to untwist itself, and was again propelled by the 

 L 1 2 magnetic 



