300 Mr R. Adie on Electrical Experiments. 



A C, and in lieu placed a bar of bismuth, 8 inches long, and .2 of 

 an inch square. The naked bulbs of two small thermometers were 

 put, one near each end, touching the upper surface of the bismuth, 

 and fastened down to the bar by a single fold of thick soft cloth tied 

 round with thread ; this effectually prevented the exposure of any 

 part of the bulbs to the air, while the coverings of both were as 

 nearly as possible equal. I may here mention that I have found 

 this method of applying thermometers to test the temperatures of 

 different parts of electrified bars, worthy of every reliance ; for, in no 

 instance, through a number of trials, has the result of the reversed 

 poles ever contradicted the first differences in temperature shewn. 

 The bismuth bar, with its attached thermometers, was allowed half 

 an hour to settle in temperature, then it was connected to a battery 

 consisting of a single pair of zinc and silver plates, superficies in ac- 

 tion 42 inches ; after an interval of 30', the observed temperatures 

 were, — room, 46°; positive end, corresponding to A, fig. 1, 59°; 

 negative end, 54°. Another trial, room, 50°; positive end, 60°; 

 negative end, 55° ; shewing a difference of 5° betwixt the two ex- 

 tremities of a bismuth bar, when conducting the electricity from a 

 single pair of plates. 



A still more marked effect, due to an electrical current, rais- 

 ing the temperature higher at the part where it enters a medium, 

 is given by Professor Daniell. " There is another well established 

 and remarkable effect of the heating power of the voltaic current, 

 which is as yet unexplained. When the conducting wires from a, 

 powerful battery, cross one another, and are brought in contact, upon 

 separating them to a short distance, a flame will appear betM'een the 

 two, and the zincode (the positive pole) will become red-hot, and 

 •that connected with the generating metal (the negative pole) will 

 remain dark, and comparatively cool. This effect is constant, of 

 whatever metal the conducting wires may be made."* The experi- 

 ment quoted, appears to me to differ only in degree from those 

 given for fine platina wire, and a bar of bismuth ; a powerful current 

 of electricity has to pass through a short space of air ; where the 

 resistance to conduction is great, the side where it enters is highly 

 heated, while the side where it escapes from the bad conductor re- 

 mains cool. 



37. For the foregoing experiments, the wires which carried the fluid 

 from the battery to the bars of metal, where the difference of tem- 

 perature were examined, offered less resistance to the passage of the 

 electricity than those bars. I, therefore, wished to try the effect of 

 conducting wires, which would offer a greater resistance to conduc- 

 tion than the bars tested. 



Iron wires were attached to a single pair battery, superficies of 

 each plate in action 42 inches, and an 8-inch copper bar 2 of an 



• Sec Daniell's Introduction to Chemical Philosophy, page 472. 



