Light f Heat, Electricity and Magnetism. 179 



heat from the whole process, being heated only to 57° or 2°*, 

 and the tool immersed in a like quantity of water, was found 

 to increase it only half a degree. 



Exp. 43. A conducting wire, made to press against the re- 

 volving bismuth disc slightly, produced a current of 2|° to 5°; 

 but on using a disconnected turning-tool to the same side and 

 near the wire, the current was still 2i° to 5° \ and yet the tool 

 could have induced a current of 30° or 40°. On increasing 

 the pressure of the wire against the cylinder, current 6° to 9° ; 

 on using the turning-tool as before, no increase of current 

 could be perceived ; yet on applying a lighted taper at the 

 junction of tlie wire to the cylinder, current 35°. 



The turning-tool does not, therefore, augment the heat of 

 surface of the disc, so as by heat to produce a current of thermo- 

 electricity. 



Exp. 44. Attached the two galvanometer wires to the piece 

 of bismuth used in the experiments for the production of 

 thermo-electricity, one at each end. Rubbed one extremity 

 of the bismuth with force against the revolving copper disc for 

 one minute, and yet no current was indicated, which would 

 have been the case, if the heat developed by friction in these 

 cases had been the source of development of the fluid ; for 

 instantly on applying the same end to the fame of a spirit- 

 lamp, the galvanometer began to deflect. Repeated the ex- 

 periment with like results; and on removing the wire at the 

 end of the bismuth next to the copper disc, and attaching it 

 to the spring which connected the mandril with the galvano- 

 meter for mechanical electricity, a current voas instantly pro- 

 duced by the same friction. Repeated, and with like resultsf. 



Exp. 45. Repeated a similar experiment with iron. The 

 sharp iron of exp. 36 was attached to the two galvanometer 

 wires, one at each end : on turning with its sharp extremity 

 the copper disc for some time, which produced an instanta- 

 neous current in exp. 36, no deviation of the needle was at 

 all observed ; but by holding the same end of the iron for a 

 few moments in the spirit flame, a constant deviation com- 

 menced, which gradually progressed to 7|°. 



Repeated the experiment with like results : yet when the 

 end adjoining the disc was disconnected and attached to the 

 spring in contact with the mandril, i. e. the ordinary connexion 

 for mechanical electricity being made (as in 3Q), an instanta- 



Observe, tlie turnings alone whicli were made, would, as will be here- 

 after shown, heat the water nearly to this amount, and the (out would in 

 tliis instance heat the water nioie than the disc ; therefore the heat derived 

 from the disc would he less than }/■'. 



t 'l"he nictils heie employed are the crystalline, which have been shown 

 to be the only bodies evolving the phacnoniciia, copper being only a simple 

 conducting body, 



N2 



