456 SCIENCE PROGRESS 



objectionable, because they are emitted with large random velocities. There is 

 considerable trouble, also, arising from gases occluded in the various parts of the 

 tube. 



Mr. B. S. Gossling elaborated the theory of what happens in the tube, and 

 mentioned the remarkable fact that, in spite of the many difficulties, it was now 

 possible to rely on reproducing the tubes having efficiencies between plus and 

 minus 10 per cent, of the mean. 



Major Whiddinglon drew attention to the extraordinary sensitivity of the 

 beat note in heterodyne reception to variations of inductance, capacity, and even 

 of the resistance of the circuit. The beat note changes appreciably for a very 

 small percentage change in the supersonic frequency. This renders possible a 

 large number of physical measurements to a very high degree of accuracy. Such 

 data as the permeability of a gas (by its effect on the inductance), or its specific 

 inductive capacity (by its effect on the condenser) are now easily measurable. 

 The device brings a very powerful new method into the field of physical research. 



Sir O. Lodge expressed the opinion that the thermionic emission method of 

 producing electrons, being of a random character, was probably bad. He asked 

 if a radioactive electrode, or the photo-electric production of electrons, had ever 

 been tried. 



Dr. Makower replied that radioactive polonium could easily be used, but that, 

 although probably more efficient than heat, the actual output would be exceed- 

 ingly small. 



Several papers on subjects related to thermionic tubes were also read. These 

 were : " On Self -Oscillation in Valves? by Major Whiddington ; " The Produc- 

 tio7i of Luminosity in Helium by Electron Collisions? by Prof. Horton and Miss 

 D. Bailey ; and " The Ionisation of Argon and Helium by Electron Collisions? 

 by Prof. Horton and Miss A. C. Davies. In the latter paper the measurement of 

 the ionisation potentials was described, the values obtained corresponding 

 approximately to Planck's quantum hypothesis of the production of the spectrum. 

 Both Dr. Goucher and Mr. Stead, however, stated that in similar measurements 

 they had found in helium two distinct ionisation potentials, the existence of which 

 had not yet been accounted for satisfactorily. 



The Report of the Committee on Radiotelegraphic Investigations was read by 

 Prof. Eccles, who gave a preliminary statement on the results of the observations 

 on the strengths of wireless signals during the recent solar eclipse. The results 

 are not yet completely worked out, but it is already established that there was 

 great strengthening of the signals attributable to the passage of the shadow 

 between sending and receiving stations. Thus the eclipse simulated the effect of 

 ordinary darkness, although it should be noted that the effect lasted several hours, 

 indicating that the penumbral part of the shadow was almost as efficient as the 

 umbra. 



In connection with wireless telegraphy Prof. G. N. Watson read an important 

 paper on " The Diffraction of Electric Waves? With the assumptions that the 

 earth is a perfect conductor, and that it is surrounded by a dialectric of height //, 

 followed by an imperfect conductor of conductivity <r, Prof. Watson calculates that 

 theory agrees with experiment if /; 3 cr = v6j x 10", expressed in electrostatic units. 

 Taking h — ioo kilometres, the estimated height of the ionised region of the 

 atmosphere, the value of o- is about that of pure water. 



A paper by Major Vincent Smith on " Wireless Telegraphy during the War? 

 was also of considerable interest. 



Preceding the discussion on Relativity on September 12, Prof. Eddington 



