554 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



ments of the same kind. Magnets of the shapes marked 5 and 7 produce 

 the artificial fields in laboratory amperemeters and voltmeters. 



For our present purpose we may define the temperature coefficients of 

 one of these magnets as the rate of change of the whole magnetic induc- 

 tion across a given surface between the poles, when the temperature of 



f 



the magnet is raised by one degree. This can be measured with sufficient 

 accuracy, by pulling out, from a definite position between the jaws, a coil 

 of suitable shape made of manganine wire and connected with a ballistic 

 galvanometer. In order to be able to make the determinations con- 

 veniently I had a brass box made of the shape indicated in the figure. 

 The box itself was first cast in one piece, and then a slot for the coil was 



