Popular Science Monthly 



955 



changed by the short-circuit. The 

 current is increased, because of the fact 

 that the primary resistance is lowered 

 by the short-circuit, but the number of 

 turns is decreased. Usually the number 

 of ampere-turns (i. e., the number of 

 effective turns times the number of am- 

 peres) is lowered by the defect ; and since 

 the energy received by the secondary 

 circuit depends on the number of am- 

 pere-turns in the primary of the trans- 

 former, it is evident that the efficiency 

 is greatly reduced. 



Therefore, an increase in the amperage 

 of the primary circuit with a decrease in 

 the reading of the voltmeter, and a large 

 decrease in the energy of the secondary 

 circuit are good indications of a short- 

 circuit in the primary of the transformer. 

 The amount of the variations mentioned 

 will depend on the number of turns cut 

 out by the short-circuit. Often the 

 shorted section will become very hot. 



Trouble of this kind is caused by poor 

 insulation, or excessive voltage being ap- 

 plied. It depends upon the extent of the 

 puncture of the insulation as to what is 

 best to be done for repairs. Occasionally 

 the entire primary must be rewound. If 

 only slightly punctured, it is easily fixed 

 by wrapping the wire in the damaged 

 portion with insulating tape. Much 

 care must be exercised in replacing the 

 wire in its original position. 



Practicing the Code Without 

 Using a Buzzer 



FOR the amateur who wants to prac- 

 tice the code and has no buzzer, a 

 good substitute can be made from an old 

 75-ohm telephone receiver. The re- 

 ceiver is hooked up in series with a i6-c.p. 

 light and a Morse key on a iio-volt 



REC. 



LAMP — 1 



i 



o 



KEY. 



\ 



The connections for a key and tele- 

 phone receiver with an incandescent light 



alternating circuit, as shown in the 

 drawing. If the buzz is too loud a smaller 

 c.p. lamp may be used to soften the tone. 

 This method should not be tried on good 

 receivers. — Malcolm Macurda. 



How To Take Up the Slack 



in Your Aerial Wires 



^HE difficult job of getting aerial 



wires stretched evenly can be 



easily accomplished by utilizing the 



arrangement shown in the illustration. 



T 



Porcelain tube in cross-bar insulating 

 the bolt for taking up slack in wires 



It consists of a porcelain tube — an 

 ordinary unglazed tube about 3 in. long 

 will do — run through a hole in the arm 

 and the holding bolt run through the 

 tube. If bolts having long threads are 

 used, considerable slack can be taken 

 up by merely turning the nut with a 

 wrench. In putting up the wires place 

 the nut in the center of the threaded 

 portion ; then it will be easy to shorten 

 or lengthen as desired. — Lee Schertz. 



PHI 

 ^ 



Canada to Protect Her Parks with 

 Radio Service 

 IILIP E. EDELMAN of St. Paul, 

 Minn., has been engaged by the 

 Canadian Government as electrical engi- 

 neer to prepare plans for wireless tele- 

 phony and telegraphy installations over 

 the 7,000 square miles embraced by the 

 Dominion Parks of Western Canada. 

 The installation will be of a new design 

 specially adapted to the difficult moun- 

 tain service. 



The object of the installation is to 

 prevent game trespassing and to afford 

 a means of instantaneous communica- 

 tion for reporting forest fires and calling 

 for aid in territory where ordinary means 

 of communication are out of the ques- 

 tion, as is often the case in Canada. 



