Popular Science Monihly 



471 



heavy spring brass sheet. It should be 

 bent, as shown in the drawing, and held 

 securely at one end by a small wood 

 block and screws. A stout, flexible cord 

 should be fastened to the upper end of 

 the lever arm and led out to a small 

 pulley, from which it should hang within 

 reaching distance of the floor. When 

 the opening door causes the peg to strike 

 the trigger and open the circuit, the cir- 

 cuit breaker should be re-set by pulling 

 the string Although not entirely ad- 

 visable, the helical spring may be omitted, 

 and a weight suspended from the lower 

 end of the string so that when the 

 door is closed, the breaker will be re-set 

 automatically- 



Connections of the various pieces of 

 apparatus should be made as indicated 

 in the accompanying diagram. 



Briefly, the operation of the electric 

 garage door-opener, is this : When the 

 wheel of the automobile runs upon the 

 board in the pit, the car should be 

 stopped. The current from the line flows 

 through the contacts and into the motor ; 

 the pulley revolves and draws itself, al- 

 most literally, along the rope, thus open- 

 ing the door. When the door is opened, 

 the peg strikes the trigger and the cur- 

 rent flow is shut off. 



There are various other ways of in- 

 stalling the motor and driving mechanism 

 upon the garage door, but the one de- 

 scribed is undoubtedly the cheapest. 

 However, in case the clearance of the 

 automobile roof is very small — too small 

 to allow even for the small space that 

 the rope occupies — the motor may be in- 

 stalled on the door jamb, and a bicycle 

 cog mounted on the end of the shaft. 

 A long bicycle chain should pass from 

 this cog to another on the opposite jamb, 

 and one of the door pulleys attached to 

 the chain. Another method which would 

 be simpler, perhaps, than either of the 

 foregoing would necessitate only the in- 

 stallation of a magnetic release and a 

 heavy weight operating through pulleys. 

 If electricity were not convenient, a wa- 

 ter motor could be used, or a water or 

 compressed-air plunger, working on tbe 

 principle of the plunger elevators, would 

 give fairly satisfactory results. It is 

 quite evident that much originality in 

 construction is left to the builder. 



Mounting Spark-Gaps to Eliminate 

 Unnecessary Noise 



A NOVEL and very good method 

 of eliminating most of the noise 

 made by a rotary spark-gap in operation, 

 is shown quite clearly in the illustration. 

 The rotary gap, with its motor, is 

 mounted in a substantial wooden cabinet, 

 with a glass door. This cabinet is then 

 suspended on four strong spiral springs, 

 from the underside of the operating table. 

 It is advisable to have the glass door 

 on the cabinet closed tightly, so as to con- 

 fine all possible noises and vibrations to 

 the wireless room. 



The springs eliminate most of the noise made 

 by a rotary spark-gap in operation 



Winding Tuning-Coils 



A METHOD of winding tuning-coils 

 so as to increase their durability and 

 quality should be of interest to wireless 

 amateurs. Most of those who wind 

 their tuning coils and loose couplers with 

 enameled wire find that it is hard to keep 

 them from rubbing when the slider pass- 

 es over the turn. This occurred with a 

 coil which one correspondent has been 

 using and which is wound with enameled 

 wire on a hard rubber tube. 



To prevent this loosening of the turns, 

 one should, before winding the coil, 

 wind an even layer of tire tape over the 

 tube, and thereafter wind the wire over 

 it tightly. This scheme will also prevent 

 the wire from loosening much on a coil, 

 wound on a wooden core, which may 

 shrink. Soaking in paraffin also prevents 

 shrinking of wooden tubes. 



