316 Mr. J. T. Bottomley on Expansion and Contraction 



to each of the stretching weights a small extra weight, and to 

 commence a hardening process which should ultimately give 

 me the wires in a condition more stable and more suitable for 

 the proposed experiments. Accordingly two extra weights 

 were made, each about one sixth of the permanent stretching- 

 weight ; so that the lightly loaded wire carried during this 

 process -^ 4- jfe of the breaking-weight, and the heavily loaded 

 wire | + -^2 of the breaking- weight. These extra weights 

 were removed after the hardening process was complete. I 

 then arranged to have the steam turned on so as to heat up 

 the tube and the wires two or three times a day, an interval 

 of at least one or two hours being given between each heating 

 to allow the tube to cool again perfectly. At the end of each 

 operation the wires were compared. The behaviour of the 

 wires during the hardening process surprised me greatly. I 

 was quite prepared, after the preliminary experiments, to find 

 that a good many heatings and coolings might be required 

 before a permanent condition was reached ; but it required 

 over two months and more than one hundred heatings and 

 coolings before anything like permanence was reached in the 

 first pair of wires I tried. At the end of this time, to my 

 great disappointment, the heavily weighted wire broke down 

 one night, having been left perfectly safe in the afternoon*. 



A fresh pair of wires was therefore suspended about the 

 end of February last, the greatest care being taken to avoid 

 any initial disturbance of the wires, and to see that they 

 were free from visible kinks or bends of any kind ; and on 

 March 2 the hardening process was commenced on these 

 wires. As I judged from the first attempt that the desired 

 condition had been very nearly reached before the breakdown 

 took place, I considered it best not to reduce the working 

 weight, but rather to accomplish what was required by taking 

 extreme care to avoid any needless disturbance"!". In the 

 middle of April, after about 120 heatings and coolings, the 

 wires seemed to have assumed a nearly permanent condition, 

 and the extra weights were removed. The measuring- 

 apparatus, to be described immediately, had been already 

 attached ; and during ten days, from April 21 till the end of 



* I think it is probable that a copper wire hung up with perhaps two 

 thirds or three quarters of its ordinary breaking- weight attached to the 

 lower end and alternately heated and cooled would break down ; and I 

 intend to make some trials of this kind on copper wire and wires of other 

 metals. 



t I must here express my indebtedness to Mr. Thomas A. B. Carver, 

 the student in charge of these experiments, now Thomson Experimental 

 Scholar in the University of Glasgow. Without such perseverance, 

 patience, and careful manipulation as he brought to bear, these experi- 

 ments could not ha\e been carried out to a successful issue. 



