Section III, 1921 [143] Trans. R.S.C. 



1. On Some Neiv Formulae for the Direct Numerical Calculation of the 

 Coefficient of Mutual Induction of Coaxial Circles 



By Louis V. King, D.Sc, F. R.S.C. 



A formula based on the computation of arithmetico-geometrical 

 means by calculating machine was discussed by the writer some years 

 ago in a former paper. The present paper deals with a new property 

 of the arithmetico-geometrical scale which leads to an extremely 

 convergent expression for the inductance of coaxial circles lying close 

 to one another. 



2. On a New High Frequency Vibration Gakanometer 



By Louis V. King, D.Sc, F.R.S.C. 



By means of a mechanical device, the vibrations of the reed of a 

 Brown telephone receiver are optically magnified to such an extent 

 that 1,000-cycle alternating currents of a few micro-amperes may be 

 easily measured. In combination with vacuum amplifiers, currents 

 several thousand times smaller may also be measured. 



3. On the Photographic Recording and Measurement of Radio-telegraph 



Signals 



By Louis V. King, D.Sc, F.R.S.C. 



In modern methods of heterodyne reception, the incoming radio- 

 frequency current in the aerial is caused to "beat" with the oscillations 

 of a local circuit, the frequency of the resulting musical note being 

 adjustable by the tuning condenser. The high frequency vibration 

 galvanometer above referred to will give visible signals which are just 

 audible in the telephone receiver. Owing to the sharpness of re- 

 sonance of the vibration galvanometer, visual or photographic 

 reception by this means is remarkably free from static interference. 

 Various applications to practical wireless problems are discussed. 



