Page:Popular Science Monthly Volume 90.djvu/331

 Popular Science Monthly

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��well known, utilizes a ratchet arrange- ment to turn on and off the gas. The first pull turns it on and lights it, the second extinguishes the light by shut- ting off the gas.

Instead of actuating it by hand an electromagnet was made and mounted on the gas jet as shown. This magnet was wound on a brass tube 3^ in. in diameter and 2 in. long. Six layers of No. 24 gage wire were wound on it. The armature is a length of ^-in. soft iron rod, to one end of which a disk ^4 in. in diameter is fastened by means of a machine screw. The chain arm was cut off as at /I.

The regular gas lighting equipment consisting of battery and kicking coil was used. The battery consisted of four dry cells and the kicking coil was made from I lb. of No. 22-gage soft iron wire 6 in. long and covered with No. 18 insulated wire. The coil wire is made into a compact bundle and carefully in- sulated. Two heads are cut from J^-in. stock. The winding consisted of 6 layers of No. i8-gage wire — about i^ lb. being required. These were connected in series to the break mounted on the gas jet. Shunted across the battery was the solenoid and a push button.

The operation is very simple ; pushing the button energizes the magnet, drawing the core in, which pushes the contact arm over. The ratchet turns on the gas and as the contact arm passes the contact on the stem of the fixture a spark is emitted when the circuit is broken, due to the high inductance of the kicking coil. When the button is re- leased the arm flies back and the gas remains lit. A second push on the button will put the light out. This apparatus can be installed at much less cost than the usual automatic lighters, and it will be found to work equally as satisfactorily. — Thos. W. Benson.

��Measurement Units of Wireless Telegraph Inductance

WIRELESS telegraph inductances are usually measured in either millihenrys, microhenrys or centimeters. Each of these units is a subdivision of the fundamental practical unit which is named in honor of the great electrician Henry. One millihenry is equal to one thousand microhenrys, and one micro- henry equals one thousand centimeters of inductance.

��An Electric Circuit for a Freezing Alarm

WITH the simple device illustrated an alarm will be given when the temperature reaches the freezing point.

���The expansion caused by the freezing of the water makes the electrical contact

A block of wood 4 in. long, 3 in. wide and 2 in. thick makes the base A. A small hollow rubber ball B is glued in block A with about one-third of the top cut off. A ver^^ thin strip of sheet copper D is placed against side of ball B and fastened to base A with screw G. Another piece of thin copper E is placed on the base by means of a screw F. This piece of copper should come within 1/32 in. of touching the copper D. The ball B is then filled with water, to C. When the temperature becomes freezing a thin coat of ice freezes over water C in ball B, causing the rubber ball to expand and push copper D out against copper E which closes the circuit. — Wm. Harrier.

��Makeshift Motor Starting Box for Bumed-Out Rheostat

ONE of the questions that is often put to applicants for commercial radio licenses is: "In case your motor starting rheostat should be damaged beyond repair, what would you use as a substitute?" The answer to the question usually is: "I would use an

���Iron plates suspended in an acidulated salt water solution for a starting box

iron pail filled with a solution of salt or slightly acidulated water and an iron rod or plate."

This substitute is one that can be appHed very often in repair shops or

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