570 AUSTIN: RADIOTELEGRAPHIC TRANSMISSION 



ceiving stations, permitting sharp tuning with consequent mini- 

 mizing of interference caused by stations other than those with 

 which communication is desired. It is desirable, therefore, that 

 the logarithmic decrement, which is a measure of the decay of 

 a train of waves, be as small as possible. 



The instrument described operates in accordance with the 

 method of Bjerknes, but the task of making careful observations 

 and necessary calculations required by the Bjerknes formula is 

 eliminated. An important element of the instrument is a vari- 

 able condenser, the capacity of which varies in accordance with 

 the law of geometric progression. 



The simplified Bjerknes formula may be written as 



... Cr-C AC 

 01 ~r 09 = TT = 71 • 



c c 



where 6i is the decrement of the circuit to be measured and ^2 the 

 known decrement of the measuring instrument. Ci is the value of 

 capacity of the variable condenser at the point of resonance and C 

 is a slightly different capacity of such a value that the energy 

 in the instrument at resonance is reduced to one-half. 



Since the variable condenser in the instrument varies in ac- 

 cordance with the law of geometric progression, then for any 

 given displacement of the condenser plates the percentage 



AC 

 change of capacity -^ will be constant throughout the range 



tof motion of the condenser. It is therefore possible to attach 

 to this condenser an accurately divided scale from which values 

 of 5i 4- 82 can be read directly. Several instruments have been 

 constructed for the Army and Navy and for the radio inspection 

 service of the Department of Commerce. 



RADIOTELEGRAPHY. — Quantitative experiments in radiotele- 

 graphic transmission.^ L. W. Austin, Naval Radio- 

 telegraphic Laboratory. 



The quantitative study of long distance radiotelegraphic 

 transmission was begun by the Navy Department in 1909-10 



1 Detailed paper to appear in the Bulletin of the Bureau of Standards. 



