WIRELESS TELEGRAPHY, 



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Since then Marconi luis .steadii}' increased the height and nunilxn- of 

 the vertical wires, and also the distance to which signals can he trans- 

 mitted through fi-ee space, and in his latest tests about 50 vertical 

 wiies over 250 feet high are used, and the distance to which signals 

 are transmitted is over 2,000 miles. 



The amount of electrical energy emplo}^ed in setting up the electric 

 oscillations for a distance of, say, 200 miles is about 150 wiitts (lo volts 

 and 15 amperes), or about one-tifth of a mechanical horsepower. The 

 source of the electrical enei-gy is a storage battery, which latter is 

 usually charged by a largt^ munber of dry cells. In ])assing, it may l)e 

 remark(Hl that an oi'dinary telegraph relay may be operated 

 at a distance of 200 miles at an expenditure of o watts at 

 the transmitting end of a telegraph wire, or with one-fiftieth 

 of the energy used in operating the electric oscillator in 

 question. The actual energy required to operate the tele- 

 graph relay is about 0.2-t of a watt, the rest of the energy 

 A 1)einp" consumed in the wire itself. 



] It nuist not, however, be assumed 

 • ; from this that the coherer is a less 

 sensitive electric receiver than the 

 relay; nor will it be, when it is 

 reflected that the electrical energy 

 expended in the case of the relay 

 is, so to speak, mainly confined 

 to the wire, as, analagously, sound 

 waves are confined within a speak- 

 ing tube, whereas the electrical 

 energy of the oscillator is radi- 

 ated into space in every direction, 

 and thus but a small portion of the total energy reaches the receiv- 

 ing vertical wire. It has )>een calculated that the electrical energy 

 received on a surface 1 foot scjuare at a distance of but 1 mile from 

 the oscillator is less than one three-hundred-millionth of the total 

 energy radiated, and it may ])e noted the energy actually radiated as 

 electric waves is a mere frsiction of the energy consumed in and at the 

 oscillator. 



P^'om the results ol)tained l>y Marconi and others it appears that 

 the etiect of increasing the length of the vertical wires is to give a 

 greater radiatnig surface at the transmitting end and to present at the 

 receiving end a larger surface upon which a greatiu- luuuber of circles 

 of waves may fall, each circle of waves adding to the electrical energy 

 set up in the receiving vertical wire. This view is seemingly borne 

 out by experiments made by Marconi with a metal cylinder 4.1 feet 

 high and 1.3 feet in diameter, with which arrangement signals have 

 been transmitted over 31 miles (tig. 6). The chief object of this 



-^^ EARTH 



Fifi. 6. — Marooui's cvliiulcr traiimiiittiiifj 



