The following is a description of a device I built at my home in
Brooklyn, which not only gave us relief from the

[Illustration:  Electric Apparatus for Driving Away Cats]

nightly feline concerts, but also furnished much amusement to my friends.

I first ran two bare copper wires along the top of the fence about 1 in. apart, fastening them down with small staples, care being taken that they did not touch.  To the ends of these wires I fastened ordinary insulated bell wire, running them to the house and connecting them to the upper binding-posts of an induction coil; I then ran a wire from the lower binding-post of my coil through the batteries back to the other lower binding-post of coil, breaking the circuit by putting in an ordinary switch.  The more batteries used, the stronger the current.  The switch should always be left open, as it uses up the current very rapidly.

When “tabby” is well on the wires I close the switch and she goes the length of the fence in bounds, often coming back to see what the trouble is, thus receiving another shock.  —­Contributed by Charles L. Pultz.

** Substitute for a Drill Bit [411]

A gouge may be used as a substitute bit if a proper sized bit is not at hand.  The gouge can be placed in the brace the same as a bit.

** Drying Films [412]

The drying of photographic film in full lengths without scratching or curling is quite difficult.  Various devices are used to keep the film straight, and

[Illustration:  Pins Keep the Film Straight]

push pins or thumb tacks are supplied with almost all of them.  The illustration shows a simple and inexpensive device constructed of common wood clothespins without any metal pins to come in contact with the film and cause rust streaks.  A pair of pins are fastened at each end of the film by pushing one pin over the other which in turn is clamped on the film.  A string tied to the heads of one pair of pins provides a way to hang the whole on a nail.  The lower pair of pins makes a weight to keep the film straight.  —­Contributed by J. Mac Gregor, Montreal, Canada.

** Grooved Pulley Made from Sheet Tin [412]

A grooved pulley which will run true and carry a round belt may be made without the use of other tools than a compass and pair of shears, with a drill or punch for making two rivet holes.

Layoff a circle on the tin, of the diameter desired for the bottom of the groove.  Then layoff a concentric circle of 1/4 in. greater radius.  Cut out along the lines of the large circle.  On the line of the small circle mark with a prick punch or nail a series of slight dents, about 1/4 in. apart, all the way around.  Now make cuts from the line of the large circle to these dents, stopping when the shears give the little “click” on entering the dent.  Bend the little tongues thus formed alternately to the right and left, then by shaping them with some care you will have a good running surface for the belt.  It will not make any difference if there are more tongues on one side than the other, or if they are not equally spaced, within reason.