Page:Popular Science Monthly Volume 91.djvu/618

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��Popular Science Monthly

��nections. After closing the old air outlet of the casing, fill the pump chamber with water, and push the plunger through the hole in the plug. After the rheostat has been connected in an electrical circuit, a resistance of varying degrees may be obtained by merely manipulating the pump handle. This apparatus is very useful for experimental work, where it is necessary to have a very careful regulation of the cur- rent. K. M. COGGESHALL.

��Transmitting Wireless Messages Underground Without Aerial

WIRELESS messages can be transmit- ted without any aerial by using at each station two ground terminals not less than 200 ft. apart. One ground should ex- tend but a few feet below the surface of the earth; the other should be sunk to a much greater depth, or better still, attached to a gas or water pipe. The receiving instruments are the same as when an aerial

���A transmitting set with ground connections for sending messagas without an aerial

is used, but at the transmitter a buzzer replaces the spark coil. An ordinary buzzer may be used with a thumb screw to tighten the armature so as to obtain a shrill hum rather than a buzz. A taut piano wire is even better than an armature. A small, portable outfit can send and receive up to five miles by using a water- pipe ground, or up to three miles by using two ground rods at about 50 ft. apart. In the country, where there are no local electrical disturbances such as those caused by trolley cars, a tuner is unnecessary. For station work a tuner should be used, and an army field buzzer generating high frequency currents will considerably in- crease the sending radius.

��Using an outfit very similar to the one described, Dr. H. Barringer Cox, of Santa Barbara, California, has succeeded in sending signals some forty miles. Ke

���Ground

��Diagram of connections with the instru- ments and the ground for the wireless set

declares that with a few slight changes he will be able to increase his sending radius to twice that distance. When perfected, this system may be valuable in military field work, as it does away with the necessity for laying a telegraph line or erecting an aerial. — J. E. Hasty.

��A Flexible Spline Used for a Draughtsman Curve

IF one adjustable curve could be ob- tained draughtsmen would readily ap- preciate its value and prefer it to others. The illustration shows such an adjustable curve-making device that is simple and convenient. With this device it is possible to obtain a great variety of curves quickly and easily, that will fit to a fraction of a degree. Another advantage of this curve is that an arc of a given radius may be drawn any length desired.

���A curve that is adjustable to a fraction of a degree to make an arc of a given radius

The curved piece A may be made of steel or suitable celluloid. The fine

threaded rod B connects the ends of the bow at C and C. A thumbscrew E is used for adjusting the bow to obtain the required curve. The device may be made in any size. — Ney.

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