Page:Popular Science Monthly Volume 88.djvu/969

 Popular Science Monthly

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��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.

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