452 



Popular Science Monthly 



distance of five hundred or a thousand 

 feet; with larger aerials even greater 

 distances can be covered. Begin in a 

 small way, however, and make your 

 progress a step at a time. 



If you are near a commercial or Naval 

 wireless station you will be able to 

 receive signals from it by using the 

 apparatus of Fig. 4; belter arrange- 

 ments which will operate over longer 

 distances will be explained in later 

 articles, however. The microphonic 

 detector of Fig. 3 is quite useful when 

 connected to a commercial wireless 

 tuner, and knowing how easily it may 

 be built from material commonly at 

 hand may be of value even to _ the 

 commercial wireless operator, in times 

 of emergency. 



You will hnd it important to become 

 a good telegraph operator if you propose 

 to continue wireless experimenting. 

 There are a number of pamphlets and 

 books published which explain methods 

 of learning 4:he Morse code; Chapter IV 

 of "The Book of Wireless," by A. Fred- 

 erick Collins, gives a good method to 

 follow. Cards showing the International 

 Morse Code in full may be obtained 

 from the Radio Inspectors' offices at 

 Boston, New York, Baltimore, Savan- 

 nah, New Orleans, San Francisco, Cleve- 

 land and Chicago. It is only by con- 

 stant practice that you can become 

 proficient. 



( To be continued ) 



A Rotary Adjustment for Coupling 



ASIMPLE method of building a 

 rotary adjustment for coupling of 

 receivers is shown in the drawing, where 

 A is the primary coil, B the .secondary 

 coil, and C indicates the slide rotls for the 

 secondary. At D is shown a small 

 square brass rack which meshes with a 



small pinion about ]/2 in. in diameter 

 at /•". The pinion is carried on shaft J, 

 which is su[)ported in small angles made 

 of 1/16 in. sheet brass, as shown at H. 

 A hard rubber or fiber knob is shown at 

 G. The rack D may also be attached 

 to the secondary coil with a small angle 

 of i/i6-in. brass. A hole should be 

 bored through the end-piece / to permit 

 D to slide through. The brass rack and 

 pinion may be purchased from an\' 

 dealers in model supplies. The arrange- 

 ment will be found well worth the trouble 

 of making, since a very fine adjust- 

 ment of coupling may be invariably 

 obtained. — C. H. R.wschenberg. 



±x. 



■^.-J 



51* Hm <//iix*, Sijffiffnon 



A Curious Form of Dustproof 

 Detector Cup 



T is well known that detectors of the 

 mineral type rapidly depreciate in 

 sensitiveness when the minerals become 



I 



covered with dust, 

 endeavor to 

 nuisance by 

 detector with a 



A great many 

 overcome this 

 co\cring llie 

 jeweler's glass 



ArranRcmcnt of Coils in Rotary Adjust- 

 ment for the Coupling Receivers 



COUNTS fIBORL IN WOOD 



Scheme to Protect Detectors of the Min- 

 eral Type from Dust 



bell or by other means. A new scheme 

 is shown in the drawing. The mineral 

 cups are placed on a brass bar or disk. 

 .1, supported by an adjustable threaded 

 rod B. 



A fine "cat-whisker" wire contact 

 point of the usual lyjie ma\- be placeil 

 on a brass spring C, which has its ten- 

 sion adjustable by means of a threailed 

 rod anil knob D. At first this may 

 seem a little inconvenient, but it really 

 is just as easy to adjust as if the min- 

 eral cups were facing uinvard, as in most 

 detectors. This is because the sensiti\c 

 si)ots DU the miner, d arc loimd b\- feel- 

 ing around with "cat-whisker" contact. 



