Electrical Resistances of Metallic Wires. 



437 



After making these corrections, the changes in the resist- 



ance remaining unaccounted for are: — 



Metals. 



Of the increase 



on the original 



resistance. 



Of the actual observed 

 change. 



Iron 



2'3 per cent. 

 1-27 „ 

 1-18 to 1-42 per cent. 

 1-23 to 216 

 0-77 to 2-206 „ 

 0-054 to 0-171 „ 

 1549 per cent. 



81 64 per cent. 

 2-91 

 57-58 to 60-7 per cent " 

 23-6 to 42-4 „ 

 41-15 to 72-01 „ 

 11-89 to 21-6 „ 





Copner 



Zinc 



Aluminium 



German silver (annealed) . . . 

 Ma°Tiesium No. 2 





With magnesium No. 2, from a different sample from No. 1, 

 the wire became shorter ; and the resistance, which should 

 have fallen '0745 percent., actually increased 1*475 per cent., 

 being equivalent to a difference of 1*549 per cent, on the 

 original resistance unaccounted for. 



With magnesium No. 1 the actual increase of resistance 

 amounted to 2*16 per cent, on the original resistance, whereas 

 theoretically it should have increased 3*39 per cent., or 1*23 

 per cent, greater than really took place ; or we may say that 

 of the theoretical increase only 54 35 per cent, was visible, 

 showing that the specific conductivity of the wire had risen. 

 Four portions of this wire were tested, and the results were 

 all very near alike. 



On examining the results obtained with German silver 

 No. 5 (annealed), which after all is most likely to interest us, 

 owing to its employment in resistance-coils, we find that the 

 total increase was equal to *454per cent.; and after deducting 

 *4 per cent., which is due to increase in length and diminution 

 of section, there still remains unaccounted for *054 per cent, 

 on the original resistance, or 11*89 per cent, of the whole 

 observed change. 



With German silver (hard-drawn) the results are very 

 curious. Here the length actually decreased; and on making 

 the necessary corrections, the resistance should have shown a 

 decrease of *284 per cent.; but the actual decrease was only 

 equal to *036 per cent., not low enough by *248 per cent. ; or 

 we may say that of the theoretical decrease only 12*26 per 

 cent, was visible. 



On examining the curves from the iron wires Nos. 3 and 4, 

 it will be observed that at the commencement uncoiling pro- 

 duced a very large increase, while coiling produced a small 

 decrease ; but after sixteen operations in one case and twenty- 



