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Page:Popular Science Monthly Volume 89.djvu/153

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Popular Science MontJtly

��139

��A Delicate Crystal Detector

AN ingenious crystal detector stand whicli may prove useful has been invented and patented by J. J. Ghegan. The crystal itself C, is held in a spring- clip II, 12, extending from binding post 14 mounted upon the base 10. A cup may be used in place of the spring- clip, when it is tiesircd to mount the crystal permanently.

Contact with the sensitive point of the mineral is made through fine wire or "cat-whisker" D, which is fastened in a screw-closed slot 22 in the end of pivoted-rod M to which the adjusting knob K is attached. The rod M turns freely on pivot 21, which is supported near the end of the upright rod A. The lower end of A is in the form of a ball E, which fits closely in the spring-socket

���A crystal detector capable of very delicate and varied adjustment

made by pieces 18, 19 and 20.

As can be easily seen, the point of D can be moved in any direction by proper- ly actuating knob A'. The .several joints must be made to move smoothly but with enough friction to hold whatever position they may be forced to assume. With this design of holder not only can the point of contact be selected at will, but the contact pressure and the angle of the wire to the crystal surface may be varied widely; all the adjustments are controlled by the thumb and finger through the single knob.

Radio in the Far South

THE two southernmost radio stations in the world are at Tierra del Fuego, the extreme southern end of South America, and on Macquarie Island, South of Tasmania and New Zealand. These stations arc about as far below the equator as Sitka, Alaska, is above.

���Two practical

types of lead-in

connectors

��LrJif „■■

��A Lead-in Connector

TWO lead-in connectors of simple design are shown in the drawings. That of Fig. 2 is made by soldering binding posts, obtained from the zinc shells of old dry cells, to a piece of sheet metal as shown. Fig. 2 shows one of better electrical design in that all connections are soldered. Both will be found serviceable. — E. R. Thomas.

An Unusual Code Letter

EXPERIMENTERS who listen to messages passing to and from German or Spanish stations are often puzzled by the code- letter of four dashes. This signal represents the combination "CH" and is used as a single letter in the International Morse or Continental code. Four dashes forming one character in American Morse signify the beginning of a new paragraph. Continued practice alone will clear up the confusion on this point.

Mounting a Rotary-Gap

THE noise made by the \ibrations of the rotary-gap can be reduced to a minimum by cutting hollow rubber balls in half and placing them under the rotary-gap as shown at A A in the illustration. The sound will be greatly reduced. — E. R. Thomas.

���The addition of rubber feet reduces the noise of a rotary-gap to a minimum

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