Dixon — On Twisted Copper Wire. 647 



to have been falsified by the air which adhered to the roughened 

 surface of the wire, for on boiling the wire in water, the specific 

 gravity then found was identical with that of the untwisted 

 wire. The diameter of the wire was reduced to *0382 inch. 



On making experiments on this wire similar to those made on 

 the ordinary wire, Young's modulus was found to have increased 

 to 14,500,000, its breaking weight to 42 lbs., and 28^ lbs. were 

 necessary to produce a permanent set. 



By drawing the first wire slowly by a weight, gradually in- 

 creased to its breaking weight, Young's modulus became 15,000,000, 

 which was practically the same value as the modulus of a piece of 

 wire twisted till it broke. 



To find the effect of twisting a wire which already had a 

 permanent set, 14 feet of the drawn wire were given 3200 turns 

 of permanent twist. Now, although it increased in length, as did 

 the first wire, still its breaking weight was unaltered: Young's 

 modulus was reduced to 11,500,000 lbs. per square inch, and 21 lbs. 

 produced a permanent set. 



The next experiment shows how much the limit of elasticity 

 for bending was altered, Young's modulus being hardly changed. 

 A piece of copper wire 12 inches long and -^ inch diameter was 

 given 180 turns of permanent twist in the lathe. This wire was 

 then held horizontally by one end being clamped in a vice, while 

 from the other was suspended a light pan for carrying weights. It 

 was now found necessary to load the pan with 1 lb. to produce a 

 permanent set. For a piece of ordinary wire of the same dimen- 

 sions j- of this weight produced a permanent set. Yet in the case 

 of these two wires there was very little difference in Young's 

 modulus, the values of it being 12,500,000 and 12,000,000 lbs. 

 ■ per square inch respectively. 



When a wire had once been given a permanent set by twisting, 

 it was found that turning the wire in either direction had exactly 

 the same effect. For example, three pieces of wire, each 4 feet 

 long, broke when given 1430, 1380, and 1420 turns respectively ; 

 and when a piece of wire of the same length was first given 700 

 turns in one direction, it broke when twisted 696 times back in 

 the contrary direction. 



Wire "0398 inch diameter, when given an average of 30 turns 

 to an inch, was so brittle that it could not be wound on a 



