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 



