256 PROCEEDINGS OF THE AMERICAN ACADEinr. 



The iron was demagnetized by the transformer and the field built 

 up in three steps : 



Amperemeter Reading. Ballistic Throw. 



0.484 8.68 



0.757 7.41 



1.219 4.41 



The galvanometer varied more than usual during the first two tests. 

 If their average be taken to be used for the 1-step building-up inter- 

 vening, the correction to be applied to 20.81 is about 0.05. That is, to 

 make the 1-step building-up comparable to the 2-step and 3-step that 

 follow there must be added 0.05 giving 20.86. The two 2-step processes 

 give as the average calculated single deflection 20.81 ; the two 3-step 

 processes 20.82. As before we have no data by which the leakage cor- 

 rection may be determined. However, the 2-step and 3-step processes 

 to which it probably would not apply agree very closely. The 1-step 

 process gives a flux change higher than the other two, but this may be 

 due to the early variation of the galvanometer which would produce 

 just that error in case the leakage correction were zero. 



The maximum flux, B, was about 13,000. 



Out of the many attempts made to obtain similar data for lower 

 values of B, the two given above were the only ones of any value. As 

 a sample of the results usually obtained I off"er the following. 



The iron was demagnetized by the transformer. 



Test of Ballistic Galvanometer. 



Amperemeter Reading. Ballistic Throw. 

 14.26 22.22 



14.26 22.21 



14.25 22.17 



The iron was demagnetized by the transformer and the field built 

 up in one step : 



Amperemeter Reading. Ballistic Throw. 



11.00 20.71 



Four repetitions of the demagnetization and building-up of the cur- 

 rent gave as four successive results those recorded. 



Amperemeter Reading. Ballistic Throw. 

 11.00 20.81 



10.99 20.55 



10.98 20.51 



10.98 20.76 



