296 



Popular Science Monthly 



stead of the condenser across the inter- 

 rupter, the former custom. The battery 

 is a small case containing ten, eight am- 

 pere-hour cells of twenty volts, and the 

 secondary is connected with the dis- 

 charge electrode or oscillator mounted on 

 top of a small case within which the 



Fig. 2. The apparatus in detail. It 

 weighs, complete, about 30 lbs, for 150 

 watts, and includes one self-exciting 250 

 cycle generator with synchronized spark 

 gap, one Dubilier condenser, one 

 transformer in oil, and a loose coupled 

 tuning coil 



rest of the apparatus is fastened. The os- 

 cillator is mounted outside to take advan- 

 tage of the rush of air in the aeroplane 

 track along, thus cooling it. The aerial 

 and equivalent capacity is connected di- 

 rectly across the spark gap, thus elimin- 

 ating the necessity of tuning by means 

 of a condenser and tuning coil. The 

 arrangement is much the same as that 

 which Hertz and Marconi used in their 

 initial experiments. It will be seen, 

 therefore, that the operating circuit pro- 

 duces a natural wave without the neces- 

 sity of adjustments such as are necessary 

 for most spark transmitters. 



The primary input is about twenty 

 volts and one-half an ampere. The inter- 

 rupter produces a musical note of about 

 250 frequencies. The trailing wire, 

 which is used as the aerial, is about 150 

 feet long, and has a three-pound lead 

 weight attached to it. With this small 

 power we were able to obtain five-tenths 

 of an ampere in the aerial wire circuit. 

 the capacity of which was al^out 0.00003 

 m.f. It was found that communication 

 could be efifected a distance of fifteen 

 miles. This served the purpose very 

 well, especially for directing artillery 



fire. The receiving wireless station was 

 situated about one mile behind the guns. 

 Between the receiving station and the 

 gunners a regular telephone line was 

 set up. 



The position of the aviator is obvi- 

 ously very perilous. He must be right 

 over the enemy's trenches if he is to 

 direct every shot of the artillery. When 

 a shot falls short or long or too much 

 to the right or to the left, he flashes the 

 information at once to his station. The 

 next shot follows the course that he in- 

 dicates. This is the most effective elec- 

 trical work which has been done in the 

 Avar. 



The aeroplane employed in this dan- 

 gerous service is a two-seater contain- 

 ing a pilot and the observer. The ob- 

 server sends his messages as quickly as 

 he makes his observations. 



Another set of instruments is used, of 

 150 watts capacity, the energy being ob- 

 tained from a generator driven by the 

 engine of the aeroplane. Various in- 

 stallations are used of this capacity, 

 some utilizing direct current and some 



Fig. 3. The apparatus with a small 

 engine for portable use 



alternating current. The best instru- 

 ment in my opinion is one which has a 

 250 cycle alternator attached by a belt 

 to the gas engine. This generator is of 

 remarkably light weight and is so con- 

 structed that it is self-exciting. The 

 whole installation, including the genera- 

 tor, a closed core transformer in oil, a 

 key, condensers, loose-coupled tuning 

 coils and hot wire meter weighs com- 

 plete but 27 pounds. How remarkable 

 is this installation may be gathered from 

 the fact that the ordinary machine 



