TRANSACTIONS OF SECTION A. 549 



9. On Luminosity and the Kinetic Theory. By J. Butler BUrke, M.A. 



The object of this pcaper is to show that the phenomena of luminosity are 

 accompanied by, or dependent upon, the formation of large molecular aggregates 

 which act as centres of intense molecular force, and that the luminosity results 

 from the bombardment of these by the free corpuscles in the luminous body, 

 which in virtue of the powerful centres of force acquire a great Telocity under 

 their attraction, producing collisions of considerable violence with them. In the 

 case of phosphorescent bodies the time during which these aggregates continue to 

 exist is very much longer than in ordinary non-phosphorescent substances when 

 they are broken up almost instantaneously. 



The effect of molecular forces in the phenomena of phosphorescence is doubtless 

 one of great importance, as solids are far more phosphorescent than liquids, and 

 these far more so than gases, in which the phenomena of phosphorescence is of 

 very rare occurrence. 



There is conclusive evidence that separate molecules exist during the process 

 of the change of refrangibility of light. This can be shown by Stokes' method of 

 crossed prisms, by which means it is found that the period of the phosphorescent 

 light is entirely independent of that of the exciting light; the exciting rays may be 

 very high up in the ultra-violet, and yet the spectrum of the phosphorescent light 

 is the same as if the exciting light were in the blue or violet. This is a most 

 remarkable fact, and proves that the luminous vibrations are not forced. Again, 

 frorn the change of absorption during phosphorescence ' it can be deduced that the 

 luminosity is due to the formation, for the time being, of new periods under the 

 influence of the exciting light either by dissociation or by association. 



An explanation is given, based on this theory of large aggregates, of the 

 Newall pressure glow, and of the discharge of negative electrification by phospho- 

 rescent bodies. 



The existence of separate phosphorescent molecules is shown by the fact that 

 the after-glow in a gas can be greatly increased in brilliancy and duration by 

 letting the phosphorescent gas difl'use through narrow metal tubing from tlie bulb 

 in which the discharge is produced into another similar bulb. 



The phosphorescent molecules therefore do not appear to carry a free charge 

 of electricity, yet the glowing molecules produce ionisation in the gas.- 



The existence of separate molecules of an ephemeral nature during luminosity, 

 to which it is due, shows that the free periods in a luminous gas need not be the 

 same as those in a non-luminous one, and therefore that the ratio of the specific 

 heats as determined for a non-luminous gas does not give the number of degrees of 

 freedom when the systems of molecular aggregates herein considered exist, during 

 which brief interval of time the physical and chemical properties of the substance 

 should be altered. 



The ratio of the specific heats for a gas in this state of molecular aggregation 

 will be quite different from that of the gas in its ordinary state. The state of 

 molecular condensation may be brought about by the action of ultra-violet light 

 by the passage of an electric discharge through the gas, or by molecular inter- 

 actions, giving rise to chemical actions. 



10, The Physical As^yects of a Theory of Colour Vision. 

 By F. W. Edridge-Green, M.D., F.R.C.S. 



The view which I wish to bring forward is that each optic nerve fibre is able 

 to convey impulses corresponding to all kinds of light — that is to say, a very 

 similar condition exists in the impulses which are transmitted along the optic 

 nerve to that which is accepted for waves of light previous to their entering the 

 eye. The limitation of the number of colour-sensations was thought to be 

 necessary because it seemed physically impossible that a single fibre of the optic 



' See Burke, Pldl. Trans., vol. cxci. (A). 

 •'' Burke, PML Mag., March and April 1901, 



