ropular Science Monthly 



a number of the units or pairs are con- 

 nected in series. This construction has 

 received the name of "quenched gap," 

 since when it was first used it was pre- 

 sumed to have an especially effective 

 quenching or extinguishing action upon 

 the spark passing across it. The quench- 

 ing action is now generally held to be more 

 dependent upon the correlation of circuit 

 adjustments than on the gap structure 

 itself, however, as will be explained later, 

 and the gap is merely one form of device 

 which is capable of giving extremely 

 uniform operation. This regularity of 

 operation depends largely upon the fact 

 that the current through the gap is kept 

 small, and the surfaces are kept clean and 

 parallel, so that successive discharges 

 take place from different portions of the 

 discharge plates. Thus extreme heating 

 of any one point is prevented, and the 

 gap may be relied upon to discharge at 

 a quite definite potential time after time. 



The basic operation is exactly as in 

 all the other spark gaps considered. The 

 construction shown in Fig. 44 involves 

 plates having cooling flanges, separating 

 feet and the silver sparking surfaces in- 

 dicated respectively by F, G and H, which 

 are placed face to face (spaced accurately 

 by the insulating gaskets J) in pairs as 

 shown. The entire group of from six to 

 thirty or forty units is clamped together 

 in a special form of rack. 



This quenched gap is connected into 

 the normal circuit of Fig. 41, replacing 

 the rotary gap there shown. For best 

 operation it requires a circuit adjustment 

 som.ewhat different from that used with 

 the rotary gap, since with "quenching" 

 operation the endeavor is to transfer 

 the energy of the radio frequency oscil- 

 lating currents across the transformer 

 with primary Li, into the antenna cir- 

 cuit, in the shortest possible time. Under 

 these conditions, the gap discharges so 

 regularly that a pure musical signal 

 tone is heard at the receiver. The tech- 

 nical differences between so-called "quench- 

 ing" and "non-quenching" operation 

 may be understood from a study 

 of such authoritative treatises as Ze- 

 meck's "Wireless Telegraphy"; the princi- 

 ples given in the foregoing are sufficient 

 to bear in mind during the first survey of 

 the action. The war-time student requires 

 only such a grasp of the general subject 



UMl-J 



9.5 J) 



of radio as will permit him to get into 

 practical field work at the earliest moment. 



Production of Radio Waves 



The oscillating currents of the con- 

 denser circuit (Fig. 41) are transferred 

 into the antenna and ground circuit by 

 the transformer action of coil L, upon its 

 secondary. Similar radio frequency cur- 



rents are 

 consequently 

 generated, in 

 groups, in 

 the aerial 

 wires which 

 stretch up- 

 ward to the 

 mast top. 

 These anten- 

 na currents 

 result in the 

 production of 

 radiant ether 

 waves of the 

 same radio 

 frequency. The wireless waves pass 

 outward over the surface of the earth, 

 in all directions, at the speed of 186,000 

 miles per second; some small portion of 

 the radiated wave energy reaches the 

 receiver to which the messages are sent. 

 The closing articles of this series will 

 take up the interception of the radio 

 waves at the receiving station. 



f!q.44 

 Separating feet and 

 sparking surfaces 



Mind Reading by Wireless — Try It 

 on Wise Friends 



THE mind reader bounds up every few 

 months. The feats he can perform 

 are little short of marvellous. William 

 Dubilier of New York has given the fol- 

 lowing details to the Popular Science 

 Monthly of how many of these mind 

 readers work. Any wireless enthusiast can 

 set up equivalent apparatus and obtain 

 equally good results. 



Dress yourself or a friend up as the 

 mind reader. Oriental costumes are all 

 the style in the mind-reading profession, 

 and in this case are especially necessary 

 because a Turkish or Indian turban makes 

 an excellent headpiece by which the 

 mind reader can conceal a pair of tele- 

 phone receivers clamped to his ears. 

 Around his body just beneath the shoul- 

 ders are wound some 100 turns of No. 



