The indicator-needle may be cut from stiff paper, thin sheet-fibre, or very thin cold-rolled brass or copper, the latter being commonly known as hard or spring-brass. Only one pointer is really necessary--that pointing to the front. But the weight of the material would have a tendency to upset the magnetic needle, and therefore it is better to carry an equally long tail or end, on the opposite side, to properly balance the needle.
A very weak current, passing in through the first post and out at the third, will cause the indicator to be deflected considerably, or so that it will point from 40° to 60° on either side of the zero point, according to the direction in which the current is running through the coils.
When not in use the magnetic needle should be removed from the pivot, and placed in a box or other safe place, where it will not become damaged.
A differently arranged tangent galvanometer is shown at Fig. 14. As the line of binding-posts would indicate, there are several coils of wire about the circle or hoop.
This galvanometer can be used for either strong or weak currents, since it is wound with both coarse and fine insulated wire. An upright plate of wood, seven inches wide and eight inches high, supports the hoop and compass. The top corners are sawed off, and four inches above the bottom a straight cut is made across the plate, five inches wide and arched in a half-circle five inches in diameter. A shelf of wood a quarter of an inch thick, three inches wide, and five inches long is made, and attached as a ledge in this arched opening, so that a compass three inches in diameter may rest upon it.
The shelf should be arranged so that it will hold the compass in the middle of the circle instead of at one side. The turns of wire will then be in line with the magnetic needle when the latter is at rest. A base-block seven inches long, three inches wide, and seven-eighths of an inch thick is cut and attached to the upright plate by driving screws through the bottom of the plate and into the rear edge of the base. The corners are to be cut from the front of the base, and ten small holes are to be bored half an inch out from the upright and about a quarter of an inch apart. These are for the end wires that will extend down from the coils, and from thence to the binding-post holes. Grooves may be cut in the under side of the base-block for the wires to rest, in, as shown at Fig. 15, which is a view of the inverted base.