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Mr. J. T. Bottomley. On the Effects of [June 19, 



have been hung up, one of each pair with a light stretching weight, 

 and the other with a weight equal to half its breaking weight. Marks 

 have been put upon the wires ; and a cathometer has been erected 

 opposite to a window in the tube for the purpose of observing the 

 difference of elongations in each pair of wires. 



In connexion with the commencement of these experiments we 

 gave as an experimental exercise to some of the students in the 

 Natural Philosophy Laboratory, the comparison of the stretching and 

 breaking of wires at different speeds. Interesting results followed, 

 and the investigation was then taken up systematically, and is still 

 being carried on. 



Pure soft iron wires were obtained, and were hung up with an 

 arrangement for measuring the amount of elongation. They were 

 then loaded more or less quickly till they broke, and the elongation 

 with different loads was determined. A large number of curves, of 

 which a specimen is given below, have been traced showing the 

 elongation produced by different loads under given circumstances. 

 They will be considered in detail in a future communication. 



The following is a general account of the experiments that have 

 been made. 



Lengths from the same hank of the wire, which was specially drawn 

 for the purpose, were hung up and a scale pan having been attached 

 to the lower end, weight was put on till the scale pan and added 

 weight together made up 28 lbs. This was the greatest weight that 

 could be put upon the wire in its natural condition, without causing 

 permanent elongation. The wire was generally left with this load 

 applied to it for 24 hours. Sometimes the wire ran down very 

 slightly in the 24 hours with the load, but not often. 



Some of the wires were then broken quickly. One pound was added 

 to the scale pan, say every three or every five minutes, except in cases 

 where the wire was visibly running down, when no fresh weight was 

 added till the running down stopped. Another set of wires was 

 broken by adding a pound every 24 hours ; another set was broken 

 by adding three-fourths of a pound every 24 hours ; another set 

 by adding half a pound every 24 hours ; and an experiment was 

 commenced in which a quarter of a pound was to be added each day, 

 but this was discontinued, and to this wire there was added one- 

 sixteenth of a pound, not at regular intervals, but only after the wire 

 had borne the weight on it for upwards of 24 hours without suffering 

 any perceptible elongation. When a small weight is added to a wire } 

 as was done in this case, the elongation takes place very slowly. The 

 wire goes on running down slowly, often for several days, and it was 

 in order to cause the whole effect of the previous weight to have been 

 produced before any fresh weight was added that this mode of adding 

 weight was adopted. The experiment unfortunately was brought to 



