138 



Popular Science Monthly 



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An easily constructed anchor-gap which 



may also be used as a plain gap for an 



ordinary spark-coil 



A Simple Anchor -Gap 



THE .drawing shows a simple and 

 easily' constructed anchor-gap. 

 All that is required is a porcelain cleat, 

 about I in. by 2 ins. of i/i6in. sheet brass 

 and two common battery bolts. The 

 holes are afterward sealed with some 

 insulating compound. The slot in one 

 plate facilitates fine adjustment, and 

 this gap may be used to advantage as 

 a plain gap for a small spark-coil, as well 

 as for an anchor-gap. — G. Dunfee. 



Making a Mechanical Interrupter 



MANY experimenters have trouble 

 with the vibrators on coils, since 

 \'ery few work satisfactorily. A mechan- 

 ical vibrator, run by a small motor may 

 roof.le</ ir/>ee/ ^ 



Side view of interrupter 



View from above. The vibrator can be 



made from odd pieces of metal which 



happen to be at hand 



be constructed according to the drawing 

 and will be found to eliminate many of 

 the difficulties. The faster the motor 

 runs, the higher the frequency of 

 interruption. 



This vibrator can be constructed from 

 odds and ends, as shown. The toothed 

 wheel should be made of brass, and the 

 teeth cut in with a hacksaw. The 

 vibrative arm is also brass. Soldered 

 to it is a piece of spring steel in which a 

 piece of platinum for one contact is 

 fastened. Two uprights hold the adjust- 

 ing-screw. The rest of the construction 

 can be seen from the illustration; 

 dimensions are not given, since they 

 may be chosen almost at the will of the 

 experimenter. — H. B. Pearson. 



Temporary Variable Condenser 



TH ERP2 have been described numerous 

 makeshift variable condensers; but 

 the one here shown is about the simplest, 

 and can be made in a few minutes. 



A bottle of thin 

 glass is filled with 

 some good conduc- 

 tive liquid such as 

 mercury. If 

 enough quicksiher 

 cannot be had, salt 

 and water or a so- 

 lution of sal-am- 

 moniac will an- 

 swer. An insu- 

 lated wire with the 

 end bared is thrust 

 deep into the liquid 

 and clamped with 

 the cork; this rep- 

 resents one plate of 



the condenser. The other plate is a tin 

 can or other vessel partly filled with the 

 same conductive liquid and having a 

 wire clamped on the edge. The bottle 

 is suspended by passing the wire through 

 a hole in a small [)iece of wood, and 

 plugging it at the height required. Care 

 must be taken that the liquid in the can 

 does not reach the wire extendidg from 

 the bottle. 



Of course with mercury in both and 

 with the outer receptacle made of glass, 

 the best results will be secured. This 

 simple arrangement can be made in a 

 short time, and will be found practical 

 for maiu' simple ex|)eriments. 



A simple form of 

 variable condenser 



