h to start in and make all the apparatus described,
without being able to intelligently use it in your experiments. Take up
a systematic course of simple experiments, and make your own apparatus,
as needed.

Before making any particular piece of apparatus, read what is said about
the other pieces of the same general nature. This will often be a great
help, and it may suggest improvements that you would like to have.

In case your apparatus does not work as expected, read the directions
again, and see if you have followed them. Wrong connections, poor
connections, short circuits, broken wire, etc., will make trouble. With
a little patience and care you will be able to locate and correct any
troubles that may come up in such simple apparatus.

THOMAS M. ST. JOHN.

How Two Boys Made Their Own Electrical Apparatus

CHAPTER I.

CELLS AND BATTERIES.

APPARATUS 1.

_1. Carbon-Zinc Cell._ Fig. 1. If you have some rubber bands you can
quickly make a cell out of rods of zinc and carbon. The rods are kept
apart by putting a band, B, around each end of both rods. The bare wires
are pinched under the upper bands. The whole is then bound together by
means of the bands, A, and placed in a tumbler of fluid, as given in
App. 15. This method does not make first-class connections between the
wire and rods. (See Sec. 3.)

[Illustration: Fig. 1.]

APPARATUS 2.

[Illustration: Fig. 2.]

_2. Carbon-Zinc Cell._ Fig. 2. In case you want to make your cell out of
carbon and zinc rods, and do not have any means of making holes for them
in the wood, as in App. 3 and 4, you will find this method useful. Cut
grooves, G, into one side of the wood, A, which should be about 4-1/2 x
1 x 1/2 in. The grooves should be quite deep, and so placed that the
rods will be about 1/4 in. apart. A strip of tin, T, 1/2 in. wide,
should be bent around each rod. The screw, S, put through the two
thicknesses of tin will hold the rod in place. Another screw, X, acts as
a binding-post. The zinc rod only is shown in Fig. 2. The carbon rod is
arranged in the same way. Use the fluid of App. 15.

3. Note. When the bichromate solution of App. 15 is used for cells, the
strong current is given, among other reasons, because the zinc is
rapidly eaten up. This action goes on even when the circuit is broken,
so always remove and wash the zinc as soon as you have finished.

APPARATUS 3.

_4. Carbon-Zinc Cell._ Fig. 3. The wooden cross-piece, A, i