Wadsworth — Interrupter for Large Indxiction Coils. 499 



To facilitate putting these segments in place and replacing 

 them if accidentally broken, the construction shown in fig. 2 

 was adopted. 



The hub, web, and flanged felloe of the brass wheel is cast 

 in one piece and turned up true all over, so as to be perfectly 

 balanced, even at high speeds. The insulating segments, ss', 

 each about 50° in length, are cut so as to fit the curve of the 

 outer face and are beveled off at each end as shown. They 

 are held in place by two brass or copper segments of the same 

 thickness and each 130° long,"" which are screwed down to the 

 face of the wheel A A. A piece of sheet platinum, d, about 

 jLmm thick (giving a beveled edge about l mm wide) is placed 

 between the slate and the brass at the side on which the 

 " break " occurs. 



When the surface is first built up in this manner, and after- 

 wards, whenever a new segment is put in place (which is 

 necessary only in case of an accident), the wheel is placed in 

 the lathe and the outer surface ground perfectly true with a 

 small revolving emery wheel or block of stick emery held in 

 the tool post. 



With a wheel of the construction just described, the wear,, 

 even with the heaviest currents, is inappreciable, on either the 

 brass or the slate segments, it being confined almost entirely 

 to the outer brush. By making this of spring copper and 

 mounting it as shown in fig. 2, at a small angle to the surface, 

 so that it springs into contact with the latter as it burns away, 

 no attention is required until the brush is used up, when it is 

 but the work of a moment to replace it by a new one; a 



* The object of this relatively greater length of contact interval is to allow 

 time, even at the highest speeds, for the current to rise to its full value in th© 

 primary circuit before the latter is brokeD. 



Am. Jour. Sci.— Third Series, Vol. XLVIII, No. 288.— Dec, 1894. 

 32 



