Note.—Before taking up the study of cells and the electric current, let us perform a few experiments in order to understand the construction and use of some of the apparatus needed for such study. A dry cell will be used as the source of the electricity for these first experiments, because it is convenient. You will understand its action later. Use this cell only as directed; improper use of it might spoil it.
EXPERIMENT 101. To study the effect of the electric current upon the magnetic needle.
Apparatus. A compass (No. 18); a dry cell, D C (No. 51); wires with spring connectors attached ([§ 226]) for making connections. [Fig. 66] shows a plan or top view of the arrangement. Any other form of cell will do in place of D C.
226. Electrical Connections. One must constantly join wires, connect wires with apparatus, or connect one piece of apparatus to another, to make the proper electrical connections. A very simple method of connections has been used in all the apparatus described in these experiments.
A little arrangement which we shall call a spring connector, S C, ([Fig. 61]), gives us a means of quickly making connections; that is, it does away with expensive binding-posts. It is made of brass, nickel plated, and may be used anywhere without affecting the magnetic needle.
Six or eight wires, about No. 24 gauge, each about 1½ ft. long, should be prepared with a connector at each end. You may use wire furnished (No. 53). Scrape the insulation from the ends of the wires for about 1½ inches, then twist the bare ends around the connectors as shown in [Fig. 61]. The wire should pass around tightly at least 4 or 5 times and then be twisted a little, as shown, to help tighten it. Do not put it on so poorly or in such quantity that the part, B, will spread.
227. [Fig. 62] shows how the connector should be slipped upon a thin piece of metal, M, like that on the galvanoscope, for example. The wire, W, from the apparatus itself is permanently fastened under the head of the screw, S, while the wire from any other apparatus is one of those kept on hand as above mentioned and connected with S C.
