119 



" Further Experiments on the Rupture of Iron Wire," by 

 John Hopkinson, B.A., D.Sc. 



In a paper read before this Society some weeks ago I 

 gave a theory of the rupture of an iron wire under a blow 

 when the wire is very long, differing from that usually 

 accepted practically, and an account of a few experiments in 

 confirmation. 



In the simple case considered mathematically, certain 

 conditions which have a material effect on the result are 

 wholly neglected, such as the weight hung below the clamp 

 to keep the wire tort, and the mass and elasticity of the 

 clamp ; these I have taken into consideration. 



Of course it is impossible to make experiments on an 

 infinitely long wire; we are therefore compelled to infer 

 the breaking blow for such a wire from the blow required 

 to break a short wire close to, the clamp, The wire used 

 in the following experiments was from 9 to 12 feet long 

 the clamp weighed 26 oz., and the weight at the end of the 

 wire was 61 lbs. Several attempts were made to support 

 the upper extremity of the wire on an indiarubber spring, in 

 order that the wire might behave like a long wire and 

 break at the bottom, and not be affected by waves reflected 

 from the upper clamp, but without success ; so that I was 

 obliged to fall back on the plan of discriminating the cases 

 in which the wire broke at the lower clamp from those in 

 which the wave produced by the blow passed over this 

 point without rupture and broke the wire elsewhere. 



The height observed is corrected by multiplication by the 



(M \^ 

 iTjr—^, ) where M is the mass of the falling weight 



and M' of the clamp. This correction rests on the assump- 

 tion that the clamp and cast iron weight are practically in- 

 compressible, and hence that at the moment of impact they 

 take a common velocity which is that causing rupture of 

 the wire. This assumption will of course be slightly in 

 error, and experiments were made in which leather washers 

 were interposed between the clamp and the iron weight to 

 cushion tke blow. The error produced by these washers 



