498 Wadsworth — Interrupter for Large Induction Coils. 



7?i, the revolving wheel ; oh, the two contact brushes ; TT, the 

 terminals of the primary coil ; ft, the terminals of the con- 

 denser; R, a rheostat for controlling the strength of the 

 primary current ; and r, one for controlling the speed of the 



Pip i 



motor, which is supplied with current from the same batteries 

 that feed the primary circuit. The current through the 

 primary is broken each time one of the insulating segments 

 on the circumference of the wheel passes under the contact 

 brush o / the principle of its operation is therefore the same 

 as that of the old toothed wheel interrupter. No novelty, 

 therefore, can be claimed for it, except as regards the method 

 of construction of the rotating wheel, but upon this depends 

 almost entirely its successful operation, under the severe con- 

 ditions of usage. In order that the action may be quiet, 

 smooth and regular, it is of course necessary that the surfaces 

 upon which the contact brushes slide, particularly the outer 

 one, should be continuous, as regards outline ; (i. e., not broken 

 into teeth, as in the toothed wheel interrupter), and that they 

 should be true at first, and remain so. The principal difficulty 

 which had to be overcome was that of a rapid burning away 

 of the material of which the insulating segments were made. 

 It is unnecessary to record here in detail the various methods 

 and materials which were at first employed in the attempt to 

 secure a construction which would satisfactorily resist, without 

 injury to itself, the heavy sparks of the " break." Hard 

 rubber, vulcanite, vulcanized fibre, and even mica in its ordi- 

 nary form rapidly burned or wore away. Finally cut slate 

 segments were tried and have proved completely successful.* 



* Porcelain segments would, perhaps, be even better, but the expense of making 

 them (on account of the expense of making the Decessary moulds, etc.) pro- 

 hibited their use. The slate is a very satisfactory substitute and as it is easily 

 "worked the cost is comparatively trifling 



