[ 31* ] 



XLI. On Expansion and Contraction with Rise and Fall of 

 Temperature in Wires under Elongating Stress. By J. T. 

 Bottomley, M.A., F.R.S.E., F.C.S* 



[Plate IX.] 



AT the Glasgow Meeting of the British Association in 

 1876 a committee was appointed for the purpose of 

 initiating secular experiments on the elasticity of wires ; the 

 place of the experiments being the tower of the University of 

 Glasgow. From time to time reports have been presented to 

 the British Association on the s abject of these wires ; but a 

 few words respecting them will help to introduce and to ex- 

 plain the bearings of the present short communication. 



In order to test the permanence of wires under long con- 

 tinued pulling stress, three pairs of wires — gold, platinum, 

 and palladium, were hung up, ten years ago, in a great iron 

 tube about 15 metres long, erected for the purpose. These 

 pairs are loaded, at the lower extremity, one with a heavy 

 load about half the breaking weight, and the other with a 

 light load less than one tenth of the breaking-weight of the 

 wire ; and from time to time comparisons as to length are 

 made between the two wires of each pair, a special katheto- 

 meter and proper marks on the wires being used for this 

 purpose. 



The observations on the suspended wires are made at differ- 

 ent times of the year ; and it is not possible to choose times 

 for the observations such that the temperature shall be always 

 the same ; nor is it even possible to be sure that the tempera- 

 ture from top to bottom of the great tube is approximately 

 uniform, though probably the two wires of each pair are 

 almost accurately at equal temperatures, compared from point 

 to point along their lengths. 



It is consequently desirable, for the purpose of being able 

 to interpret the meaning of these observations, to ascertain 

 whether there is any perceptible difference in the expansi- 

 bility of the same wire under small and great elongating 

 stresses. The experiments described in this paper were 

 undertaken with this object. 



A tube of tin-plate (Plate IX. fig. 1), about 5 centimetres 

 in internal diameter and 6 metres long, has been erected ver- 

 tically, being supported with the help of brackets (as shown 

 in the figure) in a convenient position, close to a staircase by 

 means of which access can easily be had to the top of the 

 tube. Within this tube two wires, cut from the same hank, 



* Cornniunicated by the Author, having been read before Section A of 

 the British Association at its recent Meeting in Manchester. 



