352 SECTIONAL TRANSACTIONS.— A. 



14. Sir Oliver Lodge, F.E.S. — Controversial Note en 



Popular Relativity. 



This note concerns the assumed necessary constancy of the 

 observed velocity of light in free space, as contrasted with 

 the universally admitttS constancy of its true velocity. The 

 author contends that there is no experimental evidence for 

 the dogma that wave-fronts are concentric with a travelling 

 observer initially situated at the source. The Michelson- 

 Morley experiment is consistent with such concentricity, but 

 does not necessitate it. The FitzGerald-Lorentz contraction 

 of matter is a perfectly valid alternative explanation. 

 Einstein's equations exercise no physical discrimination and 

 are consistent with either mode of expression. In interpretipg 

 them verbally it is safer for a physicist to postulate a special 

 property of 'matter than to attempt to foist complications 

 upon time and space. 



15. Prof. F. HoRTON and Miss A. 0. Davies. — The lonisa- 



tion of Atmospheric Neon. 



It has been found» that the following are critical electron 

 velocities for atmospheric neon :— ll'S volts and 17-8 volts 

 for the production of radiation, and 16-7 volts, 20-0 volts, 

 and 22-8 volts for the production of ionisation. The condi- 

 tions under which the different critical points were indicated 

 showed that the radiation velocity, ll'S volts, is associated 

 with the ionisation velocity, 16-7 volts, and that the radiation 

 velocity, 17'8 volts, is associated with the ionisation velocity, 

 22-8 volts. No third critical velocity for radiation, corre- 

 sponding to the ionisation velocity, 26-0 volts, was detected, 

 but it is possible that such a critical velocity occurs too 

 close to one of the other radiation velocities to be distinguished 

 separately. 



The conditions under which the various points were 

 obt-ained also showed that none of the critical velocities 

 mentioned can be attributed to the displacement of a second 

 electron from an already ionised atom. Neon is the only 

 gas so far investigated which has shown more than one 

 critical velocity for the removal of a first electron from the 

 atom. 



Further information as to the ionisation of neon was 

 sought by observing the spectrum of the luminosity produced 

 in the gas as the electron velocity was gradually increased; 

 for on the. generally accepted view the line spectrum of a 

 gas results from the recombination which occurs when 

 ionisation has taken place. It was found that the lines 

 of the first and second subordinate series types never appeared 

 Below 22'8 volts, but that under certain conditions the lines 

 of the Principal series type came in at 20"0 volts. No lines 

 in the visible spectrum were ever observed below 20'0 volts, 

 although the earlier experiments show that considerable 

 ionisation must have been occurring. 



The results of the ionisation experiments might be inter- 

 preted as indicating that atmospheric neon is a mixture of 

 different elements, since isotopes would be expected to have 

 the same critical velocities for electrons. Such a supposition 

 is, however, not borne out by the investigation of the spectrum 

 of the luminosity produced in atmospheric neon, for if there 

 were more than one element present it would be expected 

 that the complete spectrum of the element of lower ionising 

 velocity (including some lines in the visible spectrum) would 



' Proc. Roy. Soc. A, 1920. 



