464 



Dr. E. Rhoads on the Change in 



a lever, about 1*75 cm. in length, whose long arm. about 

 9 cm., carried two legs of the tilting mirror. The scale 

 was placed at a distance such that a movement of 1 mm. 

 represented a change of one ten-millionth of the 7 cm. 



Fig-. 1. 



M/PPOR 



■&==^ 



LEl/ER 



■a 



COUMTEffWElGHr 



CO/L 



CLAMP /A//V£ff T(/B£ 



SPECIMEN. 

 PLAT/NUM Tt/BE 



CLAMP, OUT£f? TUB£ 



length between the clamps. The specimen with its sur- 

 rounding tubes was placed in a coil, water-jacketed on the 

 inside, 24 cm. long, giving a field of 98 c.G.s. to the ampere, 

 constant almost to the ends o£ the specimen. This coil was 

 suspended by indiarubber so that all vibration-effects were 

 done away with. The whole was very skilfully made by 

 Mr. Pye, instrument-maker of the laboratory. The curves 

 obtained are very smooth and free from the effects of tempe- 

 rature ; but they are not always quite the same after taking 

 down the tubes, &c, and putting them up again apparently 

 the same as before. The cause of this is not clear at present. 



