410 On Resistance to the Passage of an Electric Current. 



increase of resistance from stretching, when the weights were taken off' 

 the wire did not immediately attain the resistance which it ultimately 

 settled at, but gradually recovered itself in about three minutes. 



This effect was very perceptible with the thicker wires, where heavy 

 weights were employed. I suppose the effect may, at any rate, be partly 

 attributed to the heat which would be generated when the wire recovered 

 its former volume ; but I am not at all satisfied that the whole of the effect 

 observed was due to this cause. 



The conclusions to be drawn from the experiments are : — 



1 . That the temporary increase of resistance of a wire when stretched 

 in the same direction as the current is exactly proportional to the stretch- 

 ing-force. 



2. That the increase per cent, of resistance wheu a cube of each mate- 

 rial is stretched by the same weight is greater in iron wire than in steel 

 wire, and greater in brass wire than in iron wire ; also that this increase 

 is nearly the same for different specimens of the same material. 



3. That the increase per cent., when the material is stretched to the 

 same extent, is much greater in iron and steel wires than in brass wire, 

 and is probably greater in iron wire than in steel wire. 



4. That there is a residual increase in each case, over and above that 

 which would follow from mere increase of length and diminution of sec- 

 tion, that this residual increase is much greater in iron and steel than in 

 brass, and greater in iron than in steel. 



