with tinfoil; connect one of these with the knob, and the other with the outer coating, of a charged electrical jar, when the see-saw motion will be produced. То make the toy more complete two tiny figures should be placed on the see-saw, one at each end.

GALVANIC TOYS.

A GALVANIC BATTERY.

GET a number of gallipots and some strips of zinc and copper. Place a strip of both metals in each of the gallipots, and connect, by copper wire twisted round each, the copper of one jar with the zinc of the next. Connect the two end strips (one of which must be copper and the other zinc) with each other by means of a long and tolerably stout copper wire. Pour into each jar a mixture of one part of oil of vitriol and ten of water, until about three parts full; your battery is now complete and in working order. The connecting wire will attract iron filings, and will turn a magnetic needle from its natural position.

AN ELECTRIC TELEGRAPH.

The action of the simplest form of electric telegraph

depends upon the fact that an electric current passing through a wire has the power of turning aside a magnetic needle. All that is required, therefore, for an electric telegraph is a battery, two magnets, conducting wires, and two "receiving instruments," all of which may be easily made.

THE RECEIVING INSTRUMENTS.

To make these get two stout cards and some wire covered with silk or cotton (to be procured at an electrician's for a few pence). Wind about a dozen turns of this wire into a flat coil, thus :

FIG. F.

Attach it by thread to the card, leaving both ends free. Get a piece of flat steel about the one-eighth of an inch wide and not quite so long as the coil of wire. Magnetize these by rubbing them several times with an ordinary steel magnet, and suspend them by their centres on a pivot, so that they are movable about it. This pivot must be fastened on the card, in the centre of the coil, so that the needle can move from side to

side in the coil. Now get a block of wood to serve as a stand for the card, which must be fixed in a groove in the block so that it will stand firmly in an upright position. Fix two strips of thin brass on the block, side by side in front of the card, and fasten one end of the coil to one strip, and the other end to the other strip; your receiving instrument is now complete.

THE BATTERY.

The battery may be made of two or three gallipots with strips of copper and zinc, and containing dilute oil of vitriol. These must be connected in the manner described on page 182, and the two end plates should not be connected with each other, but should have long wires attached to them, either by soldering or by twisting the wire tightly round the plates.

TO WORK THE TELEGRAPH.

Connect the two instruments by a wire, which must be attached to the same brass plate in each. Attach one of the battery wires to the unconnected brass plate of one instrument, and touch the corresponding plate of the other instrument with the other battery wire; both needles will be deflected at the

same moment. By arranging a code of signals, messages may be sent from one station to the other.

AN ELECTROTYPING APPARATUS.

Capital electrotype copies of wax impressions of seals and coins may be easily taken with the following simple apparatus. Take an ordinary tumbler and place in it a strong solution of sulphate of copper, made by dissolving two pennyworth of powdered blue vitriol in half a pint of boiling water. Make a porous cell by taking some stout brown paper and rolling it on a stick or on two fingers, fastening the side with sealingwax, and fitting a bottom to it by the same means. Place this cell in the sulphate of copper solution, and pour into it a mixture (prepared beforehand), of five parts of water and one part of oil of vitriol. In the cell place a thin strip of zinc, amalgamated by rubbing it first with weak oil Bof vitriol and then with a little mercury. Twist a piece of copper wire tightly round this zinc plate and attach to it the wax impression to be copied. The wax must be previously coated with black-lead, and polished with an FIG. G. old tooth-brush. After remaining in

A

D

B

the cell for about twelve hours a beautiful impression of the seal in copper will be obtained. A sketch of the apparatus is shown in fig. G, where AA is the tumbler, BB the porous cell, and D the wax impression to be coated.

HOW TO MAKE A PAIR OF TELEPHONES.

The materials for making these amusing instruments may be obtained, at a small cost, of any philosophical instrument maker. They comprise two wooden cases, two magnets, two "bobbins" or reels, two pieces of "ferrotype" iron, four binding screws, and a quantity of covered wire. About twenty yards of covered wire must first be wound upon the bobbins, one of which is next to be placed in the wide end of each wooden case, and the two ends of the wire must be fastened to the ends of two binding screws fixed in the narrow end of each case. In the centre of each bobbin must be fixed the magnet, the end of which must nearly, but not quite, reach to the broad end of the case. This part of the case has a large hole in it, and behind this hole must be fixed one of the plates of ferrotype iron to form a" diaphragm." When the two telephones are finished they must be connected by two lengths of covered