of Vertically-suspended Wires. 503 



And, as before. 



Hence 



a + 6=2-ll". 

 a = l-0553372 w *, 

 5 = 1-0546628*. 



When therefore the current was reversed, the value of a 

 was increased by 



1-0553372-1-0551792 ohm 



= •000158 ohm. 



This is equivalent to about 16 thousandths per cent. 



Assuming that a change of temperature of 1° C. produces 

 an alteration of *4 per cent, in the resistance, it follows that 

 the temperature of the copper wire was ^ degree C. higher 

 with an upward than with a downward current. 



The current traversing the wire was not measured, but it 

 was probably about 1 ampere. 



It will be seen from the figures in the Table, that the 

 changes which occurred in the resistance of the iron wire 

 were considerably smaller than those observed in the case of 

 copper. This was unexpected, since the thermoelectric effects 

 are, I believe, somewhat greater with iron. But the apparent 

 anomaly is obviously to be accounted for, at least in part, by 

 the higher specific resistance of iron. With the same electro- 

 motive force the current per unit of sectional area would be 

 six or seven times greater in copper than in iron, and the 

 Peltier effect is proportional to the current. To render the 

 results in the two cases strictly comparable, other less impor- 

 tant differences, such as those of specific heat and radiating- 

 power, would have to be taken into account. 



If a convenient opportunity offered it would be satisfactory 

 to repeat the experiments with much longer wires, such as 

 might be suspended in the shaft of a coal-pit or in a shot- 

 tower. The effects hitherto observed are so small that they 

 might possibly be due to accidental causes, and I publish this 

 account of them with some diffidence. 



* See note in preceding page. 



