Popular Science Monthly 



941 



An Efficient Spark-Plug Tester 



IT is a very simple matter to test a 

 spark-plug by the use of a small 

 spark-coil as shown in the accompanying 

 diagram. By placing the plug to be 

 tested across the terminals of the coil 

 and pushing the button, if the plug is 

 in working order a very bright spark 

 will jump across the gap. If the plug 

 is "dead" the circuit will either remain 

 open or else the current will flow with- 

 out making any spark. 



This method of testing is of particular 

 value in detecting short-circuits. For 

 instance, it frequently happens that the 

 insulation of the plug breaks down at 

 a point above the gap, in which case 

 the explosion caused by a plug in this 

 condition will be weak and result in 

 loss of power in the engine. Such a 

 short-circuit can be detected at once as 

 the spark will jump across at whatever 

 point the insulation is weakest. 



The trouble and annoyance of testing 

 spark-plugs by running the engine may 

 be obviated by the use of this simple 

 method of testing, easily arranged by any 

 experimenter. — H. A. Hooper. 



This apparatus is especially valuable 

 for testing short-circuits 



Connecting Dissimilar Telephone Lines 



THE diagram shows an arrangement 

 for connecting a grounded and a 

 metallic telephone circuit so that the 

 same telephone can be used on either 

 or both lines. When the switch is left 

 open on the grounded telephone circuit, 

 the extension bells remain grounded and 

 rings are received. When this switch is 

 closed and the switch on the metallic 

 line is opened, the telephone is cut in 

 on the grounded circuit and conversation 

 can be carried on over that line. If 

 both switches are left closed, rings are 



received simultaneously on both sets 

 of bells, and conversation is possible 

 over the combined circuits not only 

 from the telephone in the diagram but 

 between any other stations on the two 

 circuits. Thus, either circuit can be 

 used independently of the other, or at 

 this station the other telephones can be 

 switched back and forth if that service 

 is desirable. This will be found advan- 

 tageous on many rural lines connecting 

 with magneto switchboard exchanges. 

 It will also be of use on private party 

 lines. — J. G. Allshouse. 



The same telephone can be used on a 



grounded and a metallic telephone circuit 



with this arrangement 



Connecting Wires With Tinfoil 



PERHAPS a number of readers ex- 

 perience trouble in making a good 

 wire connection when solder is not at 

 hand. They will find the following 

 method very efficient, especially with 

 aluminum wire. 



Scrape about 8 ins. of the wire to be 

 connected. See that all the dirt, 

 corrosion, and grease are thoroughly 

 scraped off. With the aid of pliers, 

 twist the wires together very tightly. 

 A piece of tinfoil, about an inch wide, 

 should be lapped over the connection 

 twist. The tinfoil should be lapped 

 together as tightly as possible, without 

 tearing and then pressed with the fingers. 

 After this proceeding one or more 

 layers of tape are stretched over the 

 tinfoil, so that corrosion, rain, etc., will 

 not affect the connection. The tape is 

 pulled very tightly, to insure a good 

 connection of the tinfoil with the wire. 

 It is well to paint it with asphaltum. 



It should, of course, be understood, 

 that this expedient should be resorted 

 to only when solder is not at hand. 



