Conductors of Electricity, and during Electrolysis. 263 



10. Now by direct experiment, I found that three feet of 

 the thin wire could conduct exactly as well as eight feet of the 

 thick wire ; and hence it is evident that the resistances of two 

 yards of each were in the ratio of 3*4 to 1'27, which approxi- 

 mates very closely to the ratio of the heating effects exhibited 

 by the experiment. 



11. Exp. 2. — I now substituted a piece of iron wire ^h 

 of an inch thick, and two yards long, for the thick copper 

 wire used in Exp. 1, and placed each coil in half a pound 

 of water. A current of 1°*25 Q was passed through both 

 during one hour, when the augmentation of temperature 

 caused by the iron was 6°, whilst that produced by the 

 copper wire was 5°'5. In this case the resistances of the 

 iron and copper wires were found to be in the ratio of 6 to 

 5-51. 



12. Exp. 3. — A coil of copper wire was then compared with 

 one of mercury, which was accomplished by inclosing the 

 latter in a bent glass tube. In this way I had immersed, each 

 in half a pound of water, 1 1 £ feet of copper wire j T n th of an 

 inch thick, and 22| inches of mercury 0*065 of an inch 

 in diameter. At the close of one hour, during which the 

 same current of electricity was passed through both, the 

 former had caused a rise of temperature of 4°*4, the latter of 

 2 0, 9. The resistances were found by a careful experiment to 

 be in the ratio of 4*4 to 3. 



13. Other trials were made with results of precisely the 

 same character; they all conspire to confirm the fact, that 

 when a given quantity of voltaic electricity is passed through 

 a metallic conductor for a given length of timet the quantity of 

 heat evolved by it is always proportional to the resistance * 

 which it presents, whatever may be the length, thickness, shape, 

 or kind of that metallic conductor. 



14. On considering the above law, I thought that the ef- 

 fect produced by the increase of the intensity of the electric 

 current would be as the square of that element, for it is evi- 

 dent that in that case the resistance would be augmented in a 

 double ratio, arising from the increase of the quantity of elec- 

 tricity passed in a given time, and also from the increase of 

 the velocity of the same. We shall immediately see that this 

 view is actually sustained by experiment. 



15. I took the coil of copper wire used in Exp. 3, and have 

 found the different quantities of heat gained by half a pound 

 of water in which it was immersed, by the passage of electri- 



* Mr. Harris, and others, have proved this law very satisfactorily, using 

 common electricity. 



