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LIX. — ON TWISTED COPPEE WIRE. By S. M. DIXON. 



[Communicated by Professok G. F. Fitz Gerald]. 



[Read, June 1, 1887.] 



If a piece of copper wire be given a great number of turns of 

 permanent longitudinal twist, some of its physical properties are 

 found to be greatly changed. It is no longer ductile, and it breaks 

 instead of receiving a large permanent set, when it is distorted 

 beyond its limit of elasticity. 



The question naturally arises, How have the moduluses of 

 elasticity been changed by this permanent twist ? To answer this 

 the following experiments were made : — 



Some ordinary commercial copper wire, such as is used by 

 bell-hangers, was taken. Its specific gravity was found to be 

 8'915, and from this its diameter was calculated to be "0398 

 inch. This wire was then hung perpendicularly, the upper end 

 being firmly fixed to a rigid support, and on the lower end was 

 screwed a small vice, with a hook carrying a scale-pan, which 

 weighed 1 lb. A weight of 4 lbs. was placed in this, the wire 

 being thus almost completely freed from kinks. Young's modulus 

 for this wire was then found to be 8,000,000 lbs. per square inch, 

 and it could be loaded with 14 lbs. without any appreciable 

 permanent set being produced, the wire being broken by 34^ lbs. 

 Several experiments were made with more of this wire, and the 

 mean results are given in the Table at the end of this Paper. 



Twenty-seven feet of the wire were then given 4900 turns of 

 permanent longitudinal twist. The mode of twisting was as 

 follows : — One end of the wire was clamped to the armature of a 

 Gramme's magneto-electric machine, which was driven by two 

 Grove's cells. The other end of the wire was fastened to a 

 movable support. This support had to be moved slowly from the 

 Gramme, as the wire increased in length as it was twisted. The 

 number of turns given to the wire was counted by means of a 

 velocimeter held on the Gramme. The first experiment showed 

 that the specific gravity had diminished ; but this result was found 



