308 



and the bells to the line 2 ; if the switch is 

 down, the telephone will be connected to 

 the line 2 and the bells to line i . 



It is best to have the bells produce a 

 different sound on the instruments so that 

 you may tell by the sound which is ringing. 

 If a small nick is filed in one of the bells it 

 will change the tone. — A. A. Davidson. 



Popular Science Monthly 



An Electric Lamp- Socket Lock 

 Clamp and Seal 



EXPENSIVE tungsten globes are apt to 

 be a temptation to the petty thief. 

 The illustration shows a new lock for pre- 

 venting the removal of a globe from its 

 socket. It consists of a clamping-ring that 

 fits over the raised portion of the lower end 

 of the socket and is 

 held with a screw. 

 The screw-head is 

 provided with a 

 three-cornered pro- 

 jection inside of a 

 raised ring for a key 

 to enter in turning 

 the screw. Through 

 the raised portion is 

 a hole for a bit of 

 wire, the kind used 

 for seals, to be inserted. The globe cannot 

 be removed without breaking the seal and 

 using the key. 



A sealed lock-clamp 

 on an electric socket 



A Knob- Control for an Inductively 

 Coupled Tuner 



A CONVENIENT arrangement whereby 

 an inductively coupled tuner can be 

 operated by means of a round knob on a 



i r.' s ' 



FIG.l 





Manner in which the knob is'attached to the 

 shaft to operate a long slide of a tuner 



panel receiving set is shown in the drawing, 

 Fig. I. A double-grooved pulley is repre- 

 sented at A J which is locked on the stud- 

 bolt B. This bolt passes through the 

 sleeve C, which is locked on the panel D. 



The handle E is fastened to the other end 

 of the stud-bolt. The method of operation 

 is shown in Fig. 2. This arrangement allows 

 the use of a coupler which has a long slide. 



FI6.2 

 The method of operation of the knob- 

 control where the coupler has a long slide 



A heavy cord is fastened to the secondary 

 coil and passes over the two pulleys E. 

 Each end of the cord is led to a separate 

 groove in the pulleys A. The cord can be 

 fastened on the pulley by drilling small 

 holes in the flange of A and tying knots 

 securely in it. The size of pulley A is 

 determined by the length of the slide of 

 the loose coupler. — D. R. Simmons. 



Remover for Insulation 

 on Electric Wires 



TO remove, or skin the insulation from 

 a wire, cut a V-shaped slot having 

 curved sides in the end of a flat bar of 

 tool steel, as shown in the detail. For 

 practical purposes a bar of steel 3 in. long, 

 1 3^ in. wide and 3^ in. thick will be needed. 

 Two holes are drilled below the apex of 

 the slot for screw- 

 ing the cutter to the 

 workbench. When an 

 insulated wire is 

 pressed into the slot, 

 the sharp edges cut 

 through to the wire 

 and its covering is 

 readily removed by a 



quick pull downward. Removing the in- 

 — E. B. Williams. sulation from wires 



How to Make a Portable Aerial 

 for Wireless 



A COM PACT aerial that can be carried 

 in the pocket may be improvised from 

 a long steel tape measure, such as is used 

 by surveyors or building contractors. When 

 not in use it can be rolled up into its case 

 and carried in the pocket. Although steel 

 does not have the conductivity of copper, 

 such a tape has given very good results, 

 when strung from a tree or housetop to the 

 receiving set. Arlington has been heard 

 clearly in New York when this kind of an 

 aerial was employed. 



