ON GASEOUS COMBUSTION. 503 



by the members of Section A. The matter had now been carried to a 

 point at which the co-operation of physicists was absolutely essential 

 for further advance. Chemists had been compelled to acknowledge their 

 limitations by using meaningless words such as ' catalysis ' and ' con- 

 tact-action ' to conceal their ignorance. The real meaning of these 

 words might be found if the co-operation of physicists could be secured. 



Professor Armstrong regretted the absence of the engineers, who 

 were discussing, at a separate gathering', a problem which appeared, from 

 the printed report of their Committee, to be essentially physical in its main 

 features and almost identical in character with that which Sections A 

 and B were now discussing. He dwelt on the need of an understanding 

 being arrived at by chemists and physicists as to the nature of chemical 

 change — the phenomena could not well be interpreted either from a 

 purely chemical or from a purely physical point of view ; at present they 

 could not help one another because they did not understand one another ; 

 the two parties did not seem able to arrive at a common understanding, 

 nor would they until each could fully appreciate the point of view taken 

 by the other. Such meetings as that they were holding were becoming 

 of the utmost consequence to the progress of science in these days of 

 extreme specialisation. He had heard with pleasure that, at last, Pro- 

 fessor Dixon was prepared to admit that the presence of moisture was 

 at least necessary in starting the wave of explosion in a mixture of 

 hydrogen and chlorine ; the speaker thought he would ultimately be 

 obliged to admit that it was necessary throughout. 



If moisture be present initially and be instrumental in conditioning 

 the explosive wave, it must remain in the wave front and be operative 

 throughout the explosion, even supposing the gas in which the wavers 

 advancing to be dry; an excess of water, however, might well act 

 detrimentally by promoting reversals. 



It appeared to him to be now established that action could not take 

 place unless a conducting system were formed ; this was equally true of 

 ordinary cases of chemical change and of the passage of an electric 

 discharge through gases. One member of the system must be an 

 electrolyte. (Sir J. J. Thomson here interposed the remark : ' "What 

 is an electrolyte? ' and appeared to imply that any substance would 

 behave as an electrolyte if only a sufficient electromotive force were 

 applied.) Professor Armstrong insisted on the need of distinguishing 

 between electrolytes and non-electrolytes ; he then dwelt on the very 

 great importance from this point of view of Sir James Dewar's observa- 

 tion that the atmosphere of a bulb containing helium could be so far 

 purified by means of charcoal cooled by liquid hydrogen that it was 

 impossible to pass an electrical discharge across the bulb even when a 

 high potential was used, although the vanes of a Crookes' radiometer 

 mounted within it rotated merrily when a heat source was presented to 

 the bulb. He insisted on this observation as proof that conductivity 

 was conditioned not by the mere presence of gas, but of a gas in 

 association with the necessary impurity (conducting impurity) to 

 render possible the formation of conducting systems within the tube. 



[The argument is probably one of great importance in connection 

 with the assumption that electrons exist as distinct entities. The 



