THE ELECTKIC BELL. 733 



of the keeper and brass springs, and then hammered flat into the 

 enlarged entrance of the holes; the ends are then filed flush with 

 the sides of the keeper. When the strips are thus secured, one of 

 them (/ 2 ) is bent in the shape shown in the figure, and the other 

 is fastened by two short round-headed screws to a small square 

 block of wood, which is screwed to the board by a long wood-screw. 

 The hole in the little block through which this screw passes must be 

 made somewhat wider than required, so that the block can be 

 turned into the proper position before the screw is tightened. 

 Beneath the head of one of the two small screws which fix the 

 spring /, one end of the wire forming the coil of the electro-magnet 

 is fastened, the covering being of course previously removed from 

 the end of the wire which is to be clamped. The other end of the 

 spiral is clamped to the binding screw c, which also serves for 

 connecting the contrivance with one of the terminals of the battery. 

 The other binding screw, d, is connected by a wire with a piece 

 of brass m, 8 mm thick, which is bent at right angles, and has a 

 hole for the screw s. A small jam-nut is screwed upon 5, which 

 serves for tightening it as soon as it is adjusted to the proper 

 position. For the bell, either one of a large alarum clock should be 

 used, or one of the small shallow steel bells (called ' gongs '), easily 

 obtainable at the ironmonger's. To fix the bell a piece of brass 

 wire, 3 mm thick, has a screw cut upon it from one end to the other, 

 and two small nuts are prepared for it. The end of the wire is 

 screwed into the wooden support ; one of the nuts is then worked 

 down the screw to the proper height, upon this nut the bell is 

 placed, and finally secured by the second nut. The distance of the 

 bell from the board should be such that the hammer strikes about 

 the edge of the bell. 



In setting the whole up the bell is fixed first. The keeper, with 

 the springs and hammer, is then screwed to the little block. The 

 block itself is now adjusted until the distance between bell and 

 hammer is 2 or 3 mm , and fixed in that position by tightening the 

 long screw which fastens it to the support. Next the electro-magnet 

 is placed upon the support, and fixed in such a position that the 

 keeper may be very near to its poles, but not quite in contact with 

 them, when the hammer is made to touch the bell. Finally the end 

 of the screw s must be brought not only in contact with the spring 

 / 2 , but so as to press gently against it. This adjustment must 

 be made by trial, c and d being connected temporarily with the 

 poles of a cell. 



The spring / 2 , which should be somewhat less strong than/!, is 

 required for producing vigorous oscillations of the keeper and conse- 



