CONSTRUCTION OF ELECTRO-MAGNETIC ENGINE. 717 



Three holes are drilled in the horse-shoe for the apparatus 

 fig. 362, and in each of them a hollow screw is tapped ; one, in the 

 middle of the bend of the horse-shoe, receives the screw/; the two 

 others are cut into the ends of the legs. Into these, two brass 

 screws are fitted, which serve for attaching the horse-shoe to a 

 wooden support ; as shown in fig. 362 B, the screws pass through 

 holes in the wood and are tightened by nuts. The small piece of 

 metal e must be fixed exactly in the middle between a and 6. It is 

 best to use for it a short thick wood-screw, from which the head is 

 removed with the metal saw. The top is then filed smooth, and a 

 small depression made in the middle with the centre-punch, which 

 is afterwards drilled a little deeper. The piece is screwed into the 

 wood with the hand -vice before the electro-magnet a l> is fixed. 



The screw f is made of cast steel ; in the lower end of it a cavity 

 is made like that in e, and in the upper end a notch for the screw- 

 driver is made with the narrow cutting edge of the flat file. To pre- 

 vent the vibration of the screw /during the rotation of the spindle 

 it is clamped by a square nut, a so-called 'jam-nut,' which is firmly 

 screwed against the bend of the horse-shoe after /has been adjusted 

 in its proper position. 



The iron core for the straight electro-magnet cd must be 2 mm 

 shorter than the distance between the legs a and 5. A straight 

 hole is drilled accurately through the middle of it, and the hole is 

 widened with a broach until the piece of cast steel which is to serve 

 as spindle passes rather tightly through it. The ends of the spindle 

 are made conical and pointed with the file ; the points especially 

 must be filed very smooth, so that they may move in the cavities 

 of e and / with as little friction as possible. To render the motion 

 still more smooth a small drop of oil is poured into each cavity. 

 The spindle is fixed to the core by a bit of soft solder. 



The metal pieces g and h are first roughly cut with the chisel out 

 of a sheet of brass, l mm thick, and shaped by the file into the form 

 shown at G in fig. 362. The projecting parts at each end of the 

 arcs serve for fastening the pieces to the wooden support by means 

 of wood- screws with round heads. At the end of the spiral wire 

 which connects 6 with the piece #, and also at the end of the 

 terminal which leads from the screw 7j to the piece h, small loops 

 are made which are placed round two of the wood-screws ; when 

 these are turned they fix the pieces g and li on one side, and serve 

 at the same time, as shown in the figure, for clamping the ends 

 of the wires which connect the semicircular pieces with the electro- 

 magnet and the binding screw ~k. 



In order to make the ends of the spiral which glide along the sur- 



