The following instructions for constructing a hammer actuated by electricity will be found useful in making any device in which a "sucking solenoid" is required- The sizes of the parts, the gauges and proportions of the wire given, are suitable for a small hammer capable of working off a 4 volt accumulator, or off a couple of quart size bichromate batteries, con -nected up in series; but by increasing the size and varying the amount and gauge of the wire used to wind the solenoid, the size of the hammer can be increased and the winding altered to accomodate the £. M. P., E.M.F., or " voltage "of the current supplied. In order to render our instructions perfectly intelligible, we give a sectional view of the complete arrangement.

The operator will begin by procuring a piece of round soft iron, 4 in. long, 1/2 in. in diameter. This he will divide by sawing into two unequal lengths, one piece being 1 in. long, and the other 3 in. The ends of the pieces should be filed up smooth and level and the longer piece made very smooth by tubbing over with fine emery cloth. This latter piece we shall for the future call the " hammer. " A piece of thin brass tube 9 16 in. inside diameter, 3f in. in length, is now selected, into which the " hammer" can slide freely, and its inside is made quite smooth and bright by polishing with a straight round stick dipped in powdered brickdust. This being done, two " heads " or flanges, 21/4 in. in diameter, are cut out of thin brass sheet, a hole about 5/8 in. diameter put through the center of each.

The exact size of these central holes must be such as to admit the aforesaid brass tube being fitted tightly in them. These two flanges are then soldered, one at each end of the tube, so as to form a light metal reed or bobbin. To insulate this and thus prevent any chance electric leakage between the wire which has to be laid on, and the brass of the bobbin itself, it will be advisable to paste one turn of fairly stout brown paper round the tube itself, and a circlet of similar paper on the inner face of the heads.

The neatest way of effecting this latter portion is to strike out with the compasses the two circles on brown paper, cut these out, as also the 5/8 in. central apertures, and then give a radial snip with the scissors from circumference towards the center. The central tube can be pushed in this radial slit, and the paper circlet be then pasted smoothly down on the face of the flange. The operator will now require about 2 pounds No. 17 d. c. c. wire, with which he will wind this bobbin. Beginning at one end close against the flange, he will tie one end down with a bit of silk twist, leaving about 6 in. free for future attachment to a terminal, etc., and then proceed to wind the wire closely and evenly round, until he reaches the opposite flange. This will take about 56 turns of wire.

He then winds back again, always coiling in the same direction, until he returns to the first flange, and so on until he has laid on 19 layers and ends at the starting flange. Here he ties down firmly as before, the bight of wire to prevent uncoiling, cutting off any excess beyond 6 in. which will be required for connection. The bobbin having been thus wound and converted into a " solenoid " is to be fitted at its upper extremity, i. e, that at which the wire ends are situated, with the shorter piece of iron.

For this purpose a sufficient number of turns of brown paper are glued and rolled tightly round the 1 in. length of round iron until it makes a tight fit in the upper end of the brass tube. It is then painted over with a coat of thick shellac varnish, and forced into the tube until the surface of the iron rod is level with the ends of the tube. In order to give a finished appearance to the solenoid, and to prevent the wire from getting soiled or accidentally uncoiling, it will be well to give the last layer of wire a coat or two of varnish, which may be made by mixing a half tea-spoonful of Brunswick green or Chinese red powder with sufficient " white hard" varnish to produce a rather thin paint.

Tliis coat of varnish should be allowed to dry in a warm room for about 24 hours. While it is drying we proceed to make the stand for supporting the solenoid, the contact breaker and the anvil. F«>r the base of the stand a piece of any hard! well seasoned wood, 4x4x3/4 in. thick, when planed up, will serve admirably. In the center of this, to serve as an anvil, should he placed a cylindrical back of zinc, easily cast from the melted metal Hi a plaster of Paris mould, that should be held in place by a screw passing through the base from below. This anvil should be 5/8 in. in diameter and 8/4 in. in height. '

To support the solenoid centrally over the anvil at a height of 11/2 in. above it, we prepare a wooden upright 7 in. Pong by | in. square section. Having procured a ' similar piece of hard wood, 11/2 in. long, we put through it at1/2i in. from one end, a round 1/2 in. hole. We then round the upper end of our upright for a length of 8/4 in. into the shape of a peg 1/4 in. in diameter, leaving a truly square shoulder below it. We then glue the peg of the upright in to the hole just made, so that the arm stands at right angles to the upright. With a mortising chisel we cut a. 7/8 in. square hole in our base hoard at such a point along one side thereof that if the solenoid be held firmly, against the upright, the center of the solenoid shall coincide' with the center of the anvil beneath. The lower extremity of our upright is now served with a little good hot glue and inserted in the hole just made; care being taken to have it quite firm and perpendicular.

While the glue is drying we cut out of rather thin sheet brass a flat ring or "washer" 1/2 in. inside diameter,8/4 in. outside. This we push on the extremity of our hammer, (the 3 in. length of soft iron) for a depth of about 1 16 in., and solder it firmly thereto from the outside. We now slip the " hammer ", washer end outwards, and hold the solenoid centrally over the anvil, resting on one side against the cross arm of the said upright. While being held in this position the exact distance, about 21/4 in., between the face of the base board and that of the lower flange of the solenoid is measured, and a nicely squared piece of wood prepared of this length, £ in. square, that shall, when glued against the inside of the first upright, wedge the solenoid tightly in place, and at the same time not impede the free motion of the hammer and its washer up and down the solenoid tube.

If two thin brass strips, about1/4 in wide, be bound, one above and one below, round the solenoid, and then fastened to the upright by little brass screws, not only will the rigidity of this latter be greatly exalted, but the appearance of the whole will be much improved. The woodwork may now receive a coat of black cycle enamel. All that remains to be done is to make and fix the sliding switch or " conract breaker," and couple the wires up to this latter and the terminals. To make the contact breaker we procure a piece of sheet brass 1 16 in. thick, about 1 7/8 in. long, 1/2 in. wide. With a fine file we remove the central portion until we have reduced the brass to the shape of ], the inner edge of the gap in the center being made absolutely straight, 17 16 in. wide by | in. deep. The lower arm must be left 1/4 in. wide, the upper arm 1/8 in. wide.

A similar strip of brass, 1/8 in. wide, 1 7-16 in. long, is now inserted between the two arms of the gap, and soldered to them at such a distance from the back as to produce a slot that will admit of the tree passage of screws 1 16 in. diameter in the shank. It is needless to remark that the edge of this piece must be perfectly straight and parallel to the back. This contact breaker is now fastened loosely by means of two screws inserted in the slot on the side of the upright in such a position that when the hammer falls its washer pushes down the lower limb, and when it has risen to its full height it engages in the upper limb, thus drawing the contact breaker up.

Just below this sliding piece are arranged two light brass springs, pressing lightly toward the upright ;'one of these is connected to one end of the solenoid winding wire, the other being taken to a terminal on the base board for connection to battery. The of her end of the solenoid wire is taken direct to a second terminal on the base board, and is counled up to the other pole of battery. The action is as follows:

When the hammer is In its normal' position on the anvil, its weight drives the sliding contact down, so that it completes the circuit between itself and the two springs; the current circulates round the Solenoid, and the hammer is now slicked up into the tube. On reaching nearly to the top of its stroke't he washer on the hammer catches in the upper arm of the sliding contact, thus raising it and breaking contact' below. The 'hammer immediately fals, and in so doing its washer catch 8 in the lower arm, driving down the slide and re-establishing the contact.-" Hobbies."