154 



Popular Science Monthly 



of the apparatus, it may be outdistancing 

 all other sub-sea methods in range. 



The principles upon which ground wire- 

 less telegraphy works are interesting. 

 Ordinary electric current conduction is 

 the operating factor, instead of radiation 

 as in radiotelegraphy. The coils of the 

 sending buzzer are connected with two 

 grounds, as shown in the diagram. At 

 every break of the circuit caused by the 

 buzzer'armature, the inductive discharge 

 that ordinarily causes a spark at the 



A complete, practical break-in system to start 

 with in " through - the - ground " operation 



armature contacts, discharges to the 

 earth. The relative high voltage sends 

 an electric current from one plate to the 

 other. 



It is obvious that we have not merely 

 a narrow conductor between the plates, 

 but a conductor which is as big as the 

 earth! The result is that, while most of 

 the current going from one ground to the 

 other takes the straight-line route, a good 

 part of it spreads out. The lines of flow 

 in reality appear just like the lines of 

 force which are shown by iron filings 

 between two opposite magnetic poles. 



Some of these far-spreading streams 

 of current will reach the buried plates 

 of the receiving station. The leads of 

 the receiving station will "tap" these 

 streams — which are highly pulsating — 

 and a telephone will detect them. 



This at once explains why the line 

 going through the plates of one station 

 should be parallel to that going through 

 the grounds of the other. Another fact 

 that is found by experience is that the 

 further the grounds of each station are 



separated, the louder will the received 

 signals be. This second phenomenon can 

 be explained by referring to the diagram. 

 Here an ammeter is connected with a 

 battery through a metal block of high 

 resistance. This block stimulates the 

 action of the ground between the two 

 wireless stations. It is very much like 

 an ordinary shunt that is put across an 

 ammeter. The greater the resistance of 

 such a shunt, the less current will go 

 through it and the more will go through 

 the ammeter. 



Now, in placing the grounds of the 

 stations farther apart, we increase the 

 distance across the theoretical block. 

 Hence, the metal that the current must 

 cross, and the metal's resistance will be 

 increased. The ammeter will then re- 

 ceive more current. For just such reasons, 

 when the actual grounds are buried far- 

 ther apart, the telephones will receive a 

 larger current. 



In practice, you should space your 

 grounds at least twenty feet apart, though" 

 it would be much better to have them 

 separated over fifty feet. The neatest 

 and most efficient hook-up to start with 

 is shown in the diagram. Here the house 

 lighting mains are utilized, with a bank 

 of lamps to cut down the voltage. The 

 arrangement enables you to use as much 

 current as the size of the buzzer wires 

 will permit. It also enables you to use 

 the grounded side of the mains instead 

 of one which you would otherwise have 

 to make yourself. If your house is not 

 wired, however, as many as a dozen dry 

 cells, or an equivalent storage battery, 

 may be employed. You will have to make 

 two outside grounds for your station by 

 burying a few pipes in the ground. 



By providing your key with a third 

 contact, a simple break-in system is 

 obtained. The telephones shown in the 

 receiving circuit are high resistance wire- 

 less receivers. In conjunction with all 

 such high resistance telephones, your 

 spark coil should be used as a step-up 

 transformer. That is, the secondary of your 

 coil should be connected with the receivers 

 and the primary with two grounds. 



Of course, should you have a good pair 

 of telephones which are of low resistance, 

 you may use them without the spark 

 coil by connecting them directly with 

 the grounds. 



