Now connect your wires to the primary binding-posts of the coil and wind the end of one of them around the rat’s tail and start the vibrator.  Touch the other terminal to the rat’s ear and nose.  In a few minutes he will be as lively as ever.  —­Contributed by Chas. Haeusser, Albany, N. Y.

** A Simple Battery Rheostat [445]

A spring from an old shade roller is mounted on a board 4 in. wide, 9 in. long and 3/8 in. thick.  A binding-post is fastened to this board at each end, to which is attached the ends of the spring, as shown in Fig. 1.  The temper of a small portion of each end of the

[Illustration:  Battery Rheostat]

spring will need to be drawn.  This can be accomplished by heating over an alcohol lamp or in a fire and allowing it to cool slowly.  The ends are then shaped to fit the binding-posts.  A wire is connected to one of the binding-posts and a small square piece of copper is attached to the other end of the wire, as shown in Fig. 2.  When this device is placed in a circuit the current can be regulated by sliding the small square copper piece along the spring.  —­Contributed by H. D. Harkins, St. Louis, Mo.

** A Frame for Drying Films [446]

[Illustration:  Frame]

No doubt many amateur photographers are troubled about drying films and to keep them from curling.  The problem may be solved in the following way: 

Make a rectangular frame out of pine wood, 1/4 by 1/2 in., as shown in the sketch.  It is made a little wider and a little shorter than the film to be dried.  This will allow the end of the film to be turned over at each end of the frame and fastened with push pins.  Do not stretch the film when putting it on the frame as it shrinks in drying.  The film will dry quicker and will be flat when dried by using this frame.  —­Contributed by Elmer H. Flehr, Ironton, Ohio.

** A Home-Made Novelty Clock [446]

This clock that is shown in the accompanying engraving is made in scroll work, the cathedral and towers being of white maple, the base is of walnut with mahogany trimmings, all finished in their natural colors.  It has 11 bells in the two towers at the sides and 13

[Illustration:  Clock]

miniature electric lamps of different colors on two electric circuits.  The clock is operated by a small motor receiving its power from dry cell batteries.  This motor turns a brass cylinder over which runs a continuous roll of perforated paper similar to that used on a pianola.  A series of metal fingers, connected by wires to the bells, press lightly on this brass roll and are insulated from the roll by the perforated paper passing between.  When a perforation is reached a finger will make a contact with the brass roll for an instant which makes a circuit with the magnet of an electric hammer in its respective bell or forms the circuit which lights the electric bulbs as the case may be.

At each hour and half hour as the clock strikes, the motor is started automatically and the chimes sound out the tunes while the colored lights are turned on and off; two small doors in the cathedral open and a small figure comes out while the chimes are playing, then returns and the doors are closed.  —­Contributed by C. V. Brokenicky, Blue Rapids, Kansas.