312 PROCEEDINGS OF THE AMERICAN ACADEMY. 



rliictivity of iron wire is perhaps improved, and that the conductivity 

 of copper wiie is improved, that up to a certain point the wire can be 

 stretclied witliout increasing the resistance, or only increasing the re- 

 sistance very little; that beyond that point the resistance increases very 

 rapidly for a while, and then increases less rapidly. In most cases, 

 after the wire has been stretched to the point where the resistance 

 ceases to increase rapidly, the resistance appears to increase in such a 



Way, that the ratio ^ remains almost constant. 



It appears, then, that copper wire can be stretched to some 

 advantage ; that, if it is stretched too much, some of tlie advantage 

 gained is lost again. Experiments 3a and 8a are the only instances 

 where the co[)per wire appears to have lost at any time the full amount 

 of the advantage gained by stretching; but, even in these instances, 

 the wire seems to gain advantage in regard to its conductivity as the 

 stretching goes on. 



Thin copper wire being in the process of manufacture, stretched to a 

 great extent, the advantage gained by further stretching is less marked 

 than with thicker wire. It is noteworthy that the wire becomes very 

 brittle before it breaks, and assumes a definite structure like steel 

 wire. 



