1884.] of Conductors through which a Current is passing. 183 



currents there was in this series of experiments some uncertainty 

 owing to the fluctuations of the potential of the dynamo-electric 

 machine ; and, moreover, it is the less necessary for me to quote 

 these here as I hope shortly to make the whole investigation more 

 thorough and more satisfactory. 



Temperature of wires with 5 amperes passing, the temperature of 

 the air being 11 C. 



A Tin and mercury 22'5 



B Mercury 22 '5 



C Bare wire (dim) 21 '75 



D Cotton and shell-lac 



B Cotton-covered 



F Shell-lac varnish 



G Polished copper 



H Lampblack coating . 



21-5 

 21 75 

 21-8 



22-0 

 21-0 



The numbers in this table show that the permanent temperatures 

 assumed in the various cases differ wonderfully little with so great 

 differences as to clothing ; and that, at the least, there is no tendency 

 in the covered wires to attain a temperature higher than that taken 

 by the uncovered wires. With stronger currents it is made much 

 more apparent that the covering does, on. the contrary, favour loss 

 of heat by emission at the sides with a wire of the size here 

 . referred to. 



The foregoing table contains the results of experiments on five 

 copper wires of good conductivity with various coatings. In the first 



