Popular Science Monthly 



315 



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, draw- 

 ing 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 



