618 



Popular Science Monthly 



er or one of the telephone leads. Some 

 correspondents have suggested perma- 

 nently connecting one of the telephone 

 tips to the telephone diaphragm by use 

 of a small metal strip, saying that by 

 trying the several possible combinations, 

 they were successful in finding an 

 arrangement which actually reduced the 

 interference without weakening the sig- 

 nals. A variation of this method is to 

 use the metal-capped telephones and to 

 ground the cases, either directly or 

 through a condenser. Sometimes it is 

 sufficient to connect the case or one of 

 the telephone terminals to the operator's 

 body by bending a piece of tinfoil over 

 the ear-cap and connecting it to the case 

 or cord tip. It has also been found use- 

 ful to connect together the metal cases 

 and headband, as well as to connect to- 

 gether a certain one of the four tips and 

 the metal case. Which cord-tip to connect 

 in this way must be ascertained by trial. 



It has been learned that at a number 

 of stations both the induction and the 

 arc noises can be reduced if the antenna 

 is changed so as to point directly away 

 from the power lines. When the aerial 

 and the no- volt wires are parallel there 

 is, of course, the greatest inductive 

 effect between them, and when they are 

 about perpendicular the induction is 

 least. Sometimes a position not exactly 

 perpendicular gives the smallest inter- 

 ference, because of an irregularity in the 

 magnetic field around the power wires. 



Taken as a whole, the elimination of 

 arc noises remains a big problem at 

 some stations. In many cases the 

 remedies suggested above will reduce 

 the disturbances so much that they will 

 cause no trouble, but it is likely that at 

 some other stations the interference will 

 persist in spite of the hardest work to 

 get rid of it. If it becomes necessary, 

 the "balanced primary" method may be 

 tried as a last resort; in this arrange- 

 ment a small extra antenna is erected 

 near the power lines and connected to 

 ground through a second primary which 

 opposes the effects (on the secondary) of 

 the regular primary coil connected to 

 the regular receiving aerial. This more 

 complicated circuit may prove worth 

 while, since, by its use, the noises have, 

 in some cases, been almost entirely cut 

 out after the simpler plans failed. 



A Crystal Detector 



THE main advantage of this detector 

 is that a great number of sensitive 

 spots on the crystal are obtained. A co- 

 herer-stand may be used, by substituting 



Crystals 



r&it- 



A great number of sensitive points on the 

 crystal are obtained 



small galena crystals for the filings. In 

 the absence of a coherer-stand, use two 

 large binding posts, two brass rods and 

 a piece of glass tubing which will fit 

 snugly over the brass rods. The mineral 

 is prepared by placing a sensitive piece 

 of galena in a small piece of cloth and 

 then pounding the crystal into small 

 pieces. The small crystals are then sep- 

 arated from the powdered mineral, and 

 placed in the glass tube . Adjust the de- 

 tector by turning the glass tube and mov- 

 ing the brass rods until the maximum 

 sensitiveness is obtained. A buzzer is 

 used to excite the circuit in order to se- 

 cure the best adjustment easily. Great 

 care should be taken not to touch the 

 crystals with the hands, since moisture 

 or grease will decrease their sensitive- 

 ness to a great extent. 



Restoring Electric Light Bulbs 



OFTEN when the electric lights of 

 the tungsten filament type go out, 

 or burn out, it is caused by the break- 

 ing of the filament wire. When this is 

 the cause, screw the bulb into the socket 

 of a flexible cord and turn on the cur- 

 rent. By holding the bulb in a hori- 

 zontal position, manipulate it by turning 

 and rolling and tapping it with the hand 

 to cause the filament wires to cross. 

 When successful it will instantly light. 

 While lit, hold it in a quiet position for 

 a few minutes till the wires weld, after 

 which it can be used for regular service. 

 The writer has been able to recover 

 over 60% of light bulbs he has tried, and 

 they have lasted from three hours to 

 three weeks. — John Hoeck. 



