Page:Popular Science Monthly Volume 91.djvu/813

 Popular Science Monthly

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��Testing Electric Wires for High Tension Currents

MEN who work on high tension lines of electric service must be certain that the current is turned off from them. As an added precaution against the accidental throwing of the wrong switch they should securely ground the circuit until work on it is finished. Several types of more or less efficient "high tension" testers have been put on the market and most of these have been either of the "gold leaf" electro- scope or the more expensive quadrant types. All of these give negative results, because if they do not indicate the presence of high tension voltage, one of two condi- tions may exist. Either there is no current in the wire being tested, or the instrument does not work perfectly. In the first case the workman is safe, but in the second case, if he relies on the indications of his electroscope his life may be forfeited.

We are not willing to recommend as safe any of the electrostatic types of voltage indicators unless they can be positively checked immediately before and after the proposed observation. I have handled high tension circuits for years and find that a person can make an electroscope for testing the presence of high voltage with no apparatus. This may sound paradoxical,

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��but I use a very fine silk thread pulled from my necktie. If this fiber is sufficiently fine and is held by one end so that the other shall be very close to a high voltage line the free and finest end of this silk fiber will pulsate with the variations in an alternating current.

In close proximity to a high tension direct

��current wire the free end of the fine fiber will be attracted toward it. If allowed to touch it, it will become charged and will be instantly repelled. Close and caieful observation is necessary in the use of so simple a device. It cannot be depended upon to work in the wind or rain, but as an emergency electroscope it may help some reader. However, we advise a workman to check results on a circuit known to be carrying high voltage and — results or no results — play safe. — T. B. Lambert.

��Resistance in Circuit to Make Double Tone Automobile Horn

WITH a small amount of resistance placed in the circuit leading to an automobile horn or other electric signal the tone may be lowered to some extent, the number

���Changing the tone of a horn with a double contact push-button with resistance in one line

of sound waves being reduced to the amount of resistance used.

A simple way to work out this problem is to make a double contact push-button, which is clearly shown in the diagram. About 3 ft. of No. 20-gage German silver wire will be about right for the average electric signal such as used on automobiles and motorboats.

A very convenient place for the resistance can be made by cutting a groove around the base of the push-button. When the button is pressed slightly the signal will sound half-tone. Pushing the button all the way down will cause the full tone to be pro- duced. — Howard W. Peacock.

��A Strong Guy-Wire Anchor for Aerial Poles

NO mast is stronger than its weakest guying part, whether that be the guy- wire or the anchor. Only recently an amateur's 6o-ft. mast was broken to pieces in a 45-miles-an-hour gale because one of his guy-posts gave way. In this case the amateur used a 3-ft. length of 2 by 4-in. material driven in all but a few inches into the ground. This was easily uprooted by

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