Page:Popular Science Monthly Volume 92.djvu/971

 Popular Science Monthly

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��that the apparatus could be worked with one hand, leaving the other free to write the characters as they are produced. It is also possible to construct the apparatus in circular form by arranging the troughs around a conical piece and have the balls pushed one at a time up through the center of the cone to fall in one direc- tion or another down the cone and enter one or other of the troughs and then re- turn to the passage in the center to be pushed up again. It is further evident that a magnet might be arranged in con- nection with the above arrangement so that as soon as one ball made a contact after finishing its character the magnet would push up the next ball. Thus the machine would be entirely automatic and the operation continuous. This ar- rangement would make a very effectual apparatus for rapidly learning the code.

The apparatus, in order to continue to work properly, should be kept clean so that the ball will make perfect contact on the sides of the trough.

For cheap construction thin shiny tin should be used as this will not tarnish if carefully kept. A better construction is to make the angles of thin brass and have them nickel-plated. Ordinary steel ball-bearings will be satisfactory, but brass balls nickeled are better.

��Home- Made Electric Furnace for Heating with Arc Light

AN electric furnace of the arc type can 1 very easily be made by anyone from the following materials: fire clay, as- bestos fiber and water glass. A mixture of these ingredients will quickly dry and harden into a fireproof mass of low heat conductivity.

To make the furnace, select a box about 8 in. long and 4 in. square. Bore a hole a little above the center of each end just large enough to take a standard lighting carbon. Then mix some of the fire clay, asbestos fiber and water glass together, until a doughy mass is obtained and pack a layer 1 in. thick in the bottom of the box, forcing it down as firmly as possible. Now insert an ordinary glass tumbler in the center of the box and two wooden pins the size of light carbons in the holes at the ends. Around these pack as firmly as possible more of the mixture, filling the

��box completely. Smooth off the top and fill in the small cavities with a mixture of fire clay and water glass alone. In sim- ilar manner make a cover of the same size and about 1 in. thick. Place the box and

��Tumbler

���MiMure ; Tire cloy. Water gloss. Asbestos-''

Cross section of the box filled with the mixture around the pins and tumbler

contents, together with the cover, in some warm place, preferably on the top of a furnace, and allow them to dry for about ten days. At the end of that time the box may be broken away and the pins and tumbler removed. To improve its appearance the outside may be retouched with a little fire clay and water glass. The result is a very efficient arc furnace of practically indestructible material which can be used in series with a suitable re- sistance on any house lighting circuit for many experiments.

��A Simple Way of Cutting Mica V-Rings to Fit on an Armature

AN armature winder often experiences . much difficulty in cutting a V-ring from a sheet of mica so that it will fit properly. A simple method of getting an exact fit is as follows: We will assume that the bevel surface to be covered with mica is a section of a cone, the apex of which would extend to the heart of the shaft at a point which would be the inter- section of two lines, drawn as the contin- uation of the beveled surface of a V-ring, toward the heart of the shaft.

First, draw a perpendicular line, A A, on a mica sheet. Measure diameter of the large end of the V-ring with calipers. Place the measurement line, B B, at right with line, A A, taking care that the line, A A, cuts the line, B B, exactly in the center. Next, measure the diameter of the small end, and make the line, C C, parallel to, and at a distance from line

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