185 



reducing eddy currents in the copper," 

 stated that he had contributed the results 

 of a series of experiments in a letter to* 

 Industries,* in which he showed that the 

 strength or amount of eddy currents 

 depended on the speed with which the 

 wire moved into and out of the magnetic 

 field, and that they could be greatly 

 reduced by shaping the magnet-poles so 

 that the wire gradually entered and left 

 the field. The shape of the conductor, 

 and its position relative to the armature 

 core and the field-magnets, had a greater 

 bearing on the reduction of eddy currents 

 than the shape of the field-magnets ; and 

 round wire of any diameter was nearly 

 proof against eddy currents if the 

 machine was otherwise correctly propor- 

 tioned. 



Mr. A. Du Bois-Eeymond remarked 

 that some minor points in the diagrams 

 seemed open to criticism. With regard 

 to Figs. 9 and 10, he could not fully 

 comprehend the author's meaning when 

 he said, " the length O A, that is to say, 



* Vol. iv. 1888, p. M 9. 



