The wooden block F, on which the magnet is formed, is secured to a base board O, as shown in Fig. 122, and grooves are made in the edges of the clock, and corresponding holes are formed in the base to receive wires for temporarily binding the iron strips together. Opposite each angle of the block F, mortises are made in the base board O, to receive the keys d and wedges c. Each key d is retained in the mortises by a dovetail, as shown in Fig. 123. By this arrangement, each layer of the strip of iron may be held in position, as the formation of the magnet proceeds, the several keys d and wedges c being removed and replaced in around the block F. When the magnet has reached the required thickness, the wedges a are forced down so as to hold the inon firmly, then the layers of iron are closely bound together by iron binding wire wound around the magnet through the grooves c and holes in the bass board G.

The next step in the construction of the machine is the winding of the field magnet. To ensure the insulation of the magnet wire from the iron core of the magnet, the latter is covered upon the parts to be wound by adhesive tape or by cotton cloth attached by means of shellac varnish.

The direction of winding is clearly shown in Fig. 124. 5 layers of No.16 magnet wire are wound upon each section of the magnet, the winding of sections 1 and 2 being oppositely arranged with respect to each other. In like manner, the winding of sections 3 and 4 is oppositely arranged. The winding of section 1 is also opposite to that of 3, and that of 2 is opposite to that of 4. The winding begins at the outer end o the magnet, and ends at the inner end of the section. When the winding is completed, the temporary binding is removed. The outer ends of 1 and 2 are connected together, and the outer ende of 3 and 4 are connected. The inner end of 2 and 4 are connected. The innerend of 3 is to be connected with the commutator brush /. The inner end of 1 is to be connected with the binding post g, and the binding post g is to be connected with the commutator brush /.

Circuit of simple electric motor.

Circuit of simple electric motor.

The field magnet is now placed upon abase having blocks of suitable height to support it in a horizontal position. A block is placed between the coils to prevent the top of the magnet from drawing down upon the armature, and the magnet is secured in place by brass straps, as shown in Fig. 125.

The armature is wrapped with 3 or 4 thicknesses of heavy paper, and inserted in the wider part of the field magnet, the paper serving to centre the armature in the magnet. The armature shaft is levelled, and arranged at right angles with the field magnet. The posts in which the armature shaft is jour-naled are bored transversely larger than the shaft, and a hole is bored from the top downward, so as to communicate with the transverse hole. To prevent the binding of the journal boxes, the exposed ends of the armature shaft are covered with a thin wash of pure clay and allowed to dry. The posts are secured to the base, with the ends of the armature shaft received in the transverse holes. Washers of pasteboard are placed upon the shaft on the opposite sides of the posts, to confine the melted metal, which is to form the journal boxes. Babbit metal, or, in its absence, type metal, is melted and poured into the space around the shaft through the vertical hole in the post. The journal boxes thus formed are each provided with an oil hole, extending from the top of the post downward.

If, after cleaning and oiling the boxes, the shaft does not turn freely, the boxes should be reamed or scraped until the desired freedom is secured.

All that is now required to complete the motor is the commutator brushes ff. They each consist of 3 or 4 strips of thin hard rolled copper, curved as shown in Fig. 121, to cause them to bear upon the screws in the end of the hub G. The brushes are secured by small bolts to a disc of vulcanised fibre*, or vulcanite, at diametrically opposite points, as shown in dotted lines in Fig. 126and the brushes are arranged in the direction of the rotation of the armature. In the brush-carrying disc is formed a curved slot for receiving a screw, shown in Fig. 126, which passes through the slot into the post and serves to bind the disc in any position. The disc is mounted on a boss projecting from the inner side of the post concentric with the armature shaft. The brushes are connected up by means of flexible cord as shown in Fig. 125. The most favourable position for the brushes may soon be found after applying the current to the motor. The ends of both brushes will lie approximately in the same horizontal plane.

When the motor is in operation, the direction of the current in the conductor of the field magnet is such as to produce consequent poles above and below the armature.

Eight cells of plunging bichromate battery, each having one zinc plate 5 x 7 in. and 2 carbon plates of the same size, will develop sufficient power in the motor to run an ordinary foot lathe or 2 or 3 sewing machines.

The dimensions of the parts of the motor are tabulated below:

Length of field magnet (inside) .

10 1/2 in.

Internal diameter of polar section of magnet..

3 3/8

Width of magnet core..

2 1/2 ,,

No. of layers of wire to each coil of magnet..


No. of convolutions in each layer


Length of wire in each coil (approximate)..

95 ft.

Size of wire, Am. W. G...

No. 16.

Outside diameter of armature .

3 1/2 in.

Inside diameter of armature core

2 3/16 ,,

Thickness „ „ „

3/8 ,,

Width „ „

2 „

„ „ „ wound

2 1/2„

No. of coils on armature . .

12 ,,

No. of layers in each coil. .


No. of convolutions in each layer


Length of wire in each armature (approximate)....

30 ft.

Size of wire on armature, Am.


No. 16.

Length of armature shaft .

7 1/4in.

Diameter of armature shaft

9/32 ,,

,, „ wooden hub . • •

1 3/4,,

Distance between standards .

5 1/2,,

Total weight of wire in armature and field magnet..


(G. M. Hopkins,)