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 
factor ( jyp ) 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 the blow. The error produced by these washers 
