286 PROCEEDINGS OF THE AMERICAN ACADEMY. 



maintained constant at .55 amperes, the current which, with a wave 

 length of 100 meters, gives about the best average efficiency for all 

 conditions. The curves of Figure 11 show the eflect on the efficiency 

 of changing the supply current, lo- The secondary wave length was 

 maintained constant at 100 meters, and there were 4 turns on both the 

 secondary and primary of the helix. The full line curves show the 

 variations in current in amperes in the secondary circuit for three 

 values of secondary resistance, as the main supply current, /<,, is varied 

 from to 1.5 amperes. The dotted curves give the efficiencies for the 

 three curves plotted to the right hand scale. The relative magnitudes 



of the efficiencies would be slightly different for other values of -^, 



but the curves show that for 100 meters wave length in the secondary, 

 the maximum efficiency is obtained when the gap is operated on a 

 supply current of from 0.3 to 0.8 ampere, the exact magnitude of the 

 supply current for maximum efficiency depending on the resistance in 

 the secondary circuit. 



All of the data given above are for a wave length of 100 meters in 

 the secondary circuit. The shape of the curves would be similar for 

 other wave lengths but the scales different. If the secondary wave 

 length were longer the primary condenser would be larger, and the 

 supply current for maximum efficiency would be greater, but the gap 

 does not work steadily under any conditions with a supply current 

 greater than about 1.5 amperes. 



In conclusion of Part I, a few words should be said concerning the 

 variation in frequency of the secondary oscillations as the supply 

 current is changed. Although this point has not as yet been investi- 

 gated at all thoroughly, the conclusions drawn from some experiments 

 and observations show that the frequency of the oscillations increases 

 slightly, and practically linearly, as the supply current is increased. 

 This increase is from 1 per cent to 10 or 12 per cent for a change of 

 supply current from .2 to 2 amperes, and depends upon the adjust- 

 ments, the percentage increase being greater the closer the coupling, 

 and the greater the number of primary discharges per second. 



It is improbable that this change in frequency with changing supply 

 current can be attributed, as is done in the case of the Poulsen and 

 Lepel arcs, to the change in slope of the voltage-current characteristic, 

 for a change in gap length, which changes the slope of the E-I curve 

 more than a change in supply current, does not cause a detectable 

 change in frequency. If there is a change in frequency due to change 

 of gap lengtli, it is less than 1 per cent for a change of gap length from 

 .005 to 0.15 mm. 



