[ 498 ] 



LI. On the Elongation produced in Soft Iron by Magnetism. 

 By Sidney J. Lochner, Fellow, Clark University, Wor- 

 cester, Mass.* 3 



HAD it not been for recent experiments b y M. AlfOnse 

 Berget f , which apparently contradicted those of Mr. 

 Shelf ord Bidwell {, I should have deemed it a waste of energy 

 to have attempted to contribute anything further to our 

 knowledge of the subject. 



My original purpose was to confirm the experiments of 

 either one or the other, not expecting in any way to reconcile 

 the two. But I am led to believe that I have in general 

 verified the experimental results of both. 



The instrument which I employed for this investigation is 

 in its essential features a Michelson interferential refractometer. 

 It consists (fig. 1) of two mirrors, m and m\ the latter being 



Fig. 1. 



B r™"** 



* v ? 



\\ 



0- 



fastened to the free end of the bar B ; and of two parallel 

 plates of optical glass, P and P', the plate P' being lightly 

 silvered on the side away from the light L. 



The solenoid S contaius 2100 turns of number 17 copper 

 wire, wound in 7 laye:s on a glass cylinder 70 cm. long and 

 1*9 cm. in external diameter. The fixed end of the bar was 

 screwed firmly to the brass tail-piece D, which in turn was 

 both screwed and wedged in position. The free end of the 



bar carried the brass slide E ; which carried 

 This sHde, shown in cross section in fig. 

 lightly on the bearings F and F\ Every 

 precaution was taken to make this bearing 

 as free from friction as possible. The 

 object of the bearing was to prevent any 

 side-motion of the mirror and at the same 

 time deaden the vibrations which would 



the 



mirror m . 

 rested very 

 Fig. 2. 



* Communicated by the Author, 

 t Comptes Betidus, Nov. 7, 1892. 



X Proc. Roy. Soc. vol. xl. 



