Page:Popular Science Monthly Volume 92.djvu/165

 Popular Science Monthly

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��at W. The machine is now completed and ready to operate.

It is to be driven by a small motor, bolted so that the spindle turns away from the operator. The rider W is placed at a point directly below the zero on the yard stick, which should be at the left end if a right-hand thread was used. When the motor is started the spindle revolves, the rider follows the thread and moves along the threaded rod. When the rider has moved a distance of 1 in., 32 revolutions have been made by the spindle and a corresponding number of turns wound upon the coil under con- struction. When the rider has moved the full length of the yard stick, the spindle will have made 32 times 36 = 1152 revolutions. The rider is then replaced at zero and the winding and calculations continued. — H. W. Offins.

��A Homemade Electric Lantern for a Dry- Battery Cell

THIS lantern is constructed from an ordinary dry-battery cell 23^^ in. in diameter and 6 in. long, and a tin funnel 23^ in. in diameter. The spout of the funnel is removed and a small electric bulb of one volt is fastened into the funnel as shown. From a piece of heavy galva- nized sheet iron cut a strip J^ in. wide, having a length suffi- cient to make a clamp and carrying han- dle. Make a small thumb- switch of a piece of 1/64 by M-in. spring brass. This should be located near

���Handle attachment and connections to battery

��the carrying handle. An old electric bulb from an automo- bile side lamp may be used, or a one- volt lamp with a brass screw socket and a porcelain base will answer the purpose. Secure the funnel reflector to the battery with a brass clamp, and when

��the battery is used up unscrew and con- nect with a fresh one. This provides a powerful and handy electric lantern which is as easy to carry as the old barn lan- tern and which is more satisfactory. — P. P. Avery.

An Easily Constructed Variable Condenser of Brass and Tinfoil

AKE a wooden roller 3 in. in diam- eter and 4 in. long, as shown,

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���Wood roller with tinfoil half way over the surface to vary the capacity of the condenser

and mount it on a shaft, which may well be of 3^ -in. brass rod. Thread one end of the shaft so that a wooden knob and metal pointer may be screwed in place. Coat one half of the surface of the cylinder with tinfoil, and solder a fine wire connection from the foil to the shaft. The shaft should project about }/2 in. from the cylinder at one end and about 1 Yz in. at the other (which carries the knob and pointer), according to the size of the cabinet to be used.

Make a half-cylindrical piece of thin sheet brass or copper a trifle larger than the wooden cylinder, bending out support- ing feet as shown. When these two parts are finished, the condenser may be assembled.

When the knob is turned, more or less of the tinfoil is presented to the sheet of brass or copper and consequently the effective capacity is varied. Connections are made with the shaft and the fixed sheet of tinfoil and with the brass or copper shell which is around the outside of the roller. — Thos. Millsbaugh.

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