602 



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. 



