360 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



the average value of H over the cross section of the metal at the neck. 

 At the surface of a magnet the tangential components of the magnetic 



TABLE VII. 



Cylinder of Soft Stubs Polished Drill Rod. 



force are continuous, while the normal component is discontinuous : it 

 seems desirable, therefore, before one applies the method in any partic- 

 ular case, that one make sure that the lines of the field in the air space 



TABLE VIII. 

 Isthmus of Soft Stubs Drill Rod. 



to be used are practically straight and parallel to the axis of the speci- 

 men. Any person who has had experience in using large yokes at high 

 excitations, where because of the low permeability of the metal the leak- 

 age is very great, knows how slight a change in the shape of a specimen 



