The Water Circulation.—The water chamber is connected by two rubber tubes with an external tank.

The motor may be geared direct to a very small dynamo, if the latter is designed to run at high speeds.

A piston valve, being moved more easily than a box valve, is better suited for a pump of this kind, as friction should be reduced as much as possible.

Take your needle and some strong thread, and make all corners at the ends of pockets quite secure.

A good specimen of this type is so stable that if launched upside down it will right itself immediately and make a normal flight.

Note that the whole of the cane is on the under side of the top bar of the T.

This alternation is repeated over and over again, until all the energy of both pendulums is exhausted.

All tinned iron surfaces should be given a couple of thin coats or paint.

Below it is a “brush” of strip brass pressing against the tube. This brush is connected with a wire running to one terminal of a battery near the dial.

To prevent the handle bending over, solder round the pivot hole 3/4 inch of brass tubing, fitting the pivot closely.

Specify very thin zinc for the air vessel, and have the top edges stiffened so that they may remain straight.

The nearer to the hole you can wear the glass away the finer will be the line made by the pen.

This useful little article can be constructed in a couple of hours by a handy person.

Their length under the heads exceeds the inside depth of the box by the thickness of the lid.

The funniest antics are produced by very slight jerks.

The ends of the wire should be soldered together, and the ends of the link held up to the handles by a couple of staples.

A little sliding weight to place on the rod near the pencil will be found useful for keeping the pencil point in constant contact with the paper.

A thread attached to the pencil will enable you to keep the pencil off the paper until you wish to begin drawing the profile.

The upper half overlaps the lower, outside, by a quarter of an inch.

The condensed water and tar fall from the open ends of the pipes into the base.