Kff-ects of Mechanical Stress on Electrical Resistance. 291 



The order of an experiment was as follows : The test wire- BR 

 was first of all made as straight as possible by means of a small 

 weight. The sliding contact B was then moved about till there 

 was no deflection in the galvanometer. Readings were taken at the 

 points B, R, and also at a pointer, M, fixed on the wire near the top 

 of the bottom scale S. A weight of 7 Ibs. was then added to the 

 small weight, and a balance again taken. The additional weight 

 was then taken off, and a balance found. In this way, successive 

 additions of 7 Ibs. were made, and balance readings taken each time 

 till the wire broke. The distance between the wires was about 

 10 cm., and the length between B and R from 400 to 450 cm. The 

 galvanometer was made so sensitive that a movement of B of ^ mm. 

 could be distinctly detected, so that a change of ^ in 4000, that is, 

 1/160 per cent, was measurable, and allowing for small errors in 



