480 



Mr. J. L. W. Grill on the Distribution of 



From the results obtained it is observed that for any speci- 

 men the ratio of B, to B max. is constant as long as the centre 

 of the specimen is not saturated (B max. being the induction 

 at the centre) . It is also observed that this ratio varies only by 

 a small amount for specimens of different relative dimensions, 

 and is constant for all specimens 'whose length is less than thirty 

 times the section. 



When this ratio is known, the value of B x may be deter- 

 mined simply by measuring the induction at the centre of 

 the specimen. 



The value of this ratio for specimens whose length is less 

 than thirty times the section is '768. 



This method of obtaining the value of Bi can be applied 

 over the whole range of induction used in practical work, 

 since saturation does not begin below an induction density of 

 at least 10,000. While the main object of the experiments 

 was to obtain if possible some simple relation of this kind, 

 other interesting and useful results have been deduced from 

 the observations. These will be referred to later on. 



Metliod of Observation. 



The induction was determined by measuring the induced 

 current in a small search-coil C (see fig. 1) when the field 

 was reversed. 



Fig. 1. 



This coil was wound on an ebonite spool which could be 

 moved along the specimen. A d'Arsonval ballistic galva- 

 nometer G was employed to measure the induced current. 



The scale of the galvanometer was calibrated relatively by 



