432 Mr. W. E. Williams on the Magnetic Change of 



In all the experiments a curve of ascending reversals was 

 first found, and then the residual effect was found separately, 

 and the two added to get the curve of total change of length 

 or resistance. This method has the advantage that the zero 

 reading can he found before and after each separate reading, 

 and it can be ascertained whether it has changed in the in- 

 terval. The residual effect is comparatively small, and the 

 curve is a straight line for the greater part of its length. 



The magnetic change of resistance was calculated from the 

 formula 



SR _ (S + R4-100<r)&g 

 R R(S + .w) ' 



where R is the resistance of nickel wire, 

 S is the resistance of copper wire, 

 cr is the resistance of bridge-wire per cm., 

 x is the reading on the bridge. 



The results obtained are shown in the following tables and 

 the accompanying curves. 



Table I. — Change of Resistance for Various Loads, 

 -p- X 10 4 . Load in grammes. 



H. 

 10 



0. 



50. 



100. 



300. 



500. 



700. 



30 



1-5 



10 



•8 



•5 



00 



20 



10-5 



7-8 



60 



3-6 



2-1 



•4 



30 



18-5 



15-7 



135 



7-5 



4-5 



•8 



50 



312 



30-0 



261 



15-5 



9-6 



3-3 



75 



45-3 



39-6 



40 8 



25-8 



174 



72 



100 



55-2 



55*5 



53-4 



37-2 



273 



14-4 



150 



696 



726 



72-0 



596 



471 



24-3 



200 



78-0 



831 



84-7 



78-0 



660 



40-2 



250 



83-7 



91-2 



92-7 



94-9 



83-4 



55-5 



300 



88-8 



977 



990 



102-3 



103-3 



69-9 



350 



93-0 



102-9 



1080 





114-6 



84-6 



400 



963 



107'4 







124-8 



101-8 



Table I. gives the change of resistance for different loads 

 ranging from to 700 grammes. The corresponding curves 

 are shown in fig. I, the ordinates being the change of re- 

 sistance -yr- x 10 4 and the abscissse the magnetizing field in 



C.G.s. units. It will be noticed that these curves cross each 

 other, which, as is well known, is not the case with the 

 magnetization curves for these loads. 



