450 Prof. V. B. Lewes. The Cause of Luminosity [Mar. 21,. 



November 2, the flow was never less than 3,000 millions of gallons 

 per day, and on November 2 it reached 4,240 millions. Again, on 

 the 17th the flow was 3,305 millions, and on the 18th, 4,165 millions, 

 It then gradually decreased to 1,845 millions on the day when the 

 sample was drawn. Thus the Thames basin had been twice very 

 thoroughly washed out immediately before the time when the 

 November sample was taken. There had previously been no such 

 floods after the 5th of January in that year. This condition of things 

 affords a fairly satisfactory explanation of the anomalous result 

 yielded by this sample. 



III. " The Cause of Luminosity in the Flames of Hydrocarbon 

 Gases." By VIVIAN B. LEWES, Professor of Chemistry at 

 the Royal Naval College, Greenwich. Communicated by 

 Professor THORPE, F.R.S. Received February 14, 1895. 



In a paper read before the Chemical Society in 1893, I showed 

 that in the inner non-luminous zone of a flame of ordinary illuminating 

 gas, the hydrocarbons originally present in the gas, and consisting of 

 ethylene, butylene, benzene, methane, and ethane, became converted by 

 the baking action of the walls of flame between which they had to pass 

 into acetylene, and that at the moment when luminosity commenced, 

 over 80 per cent, of the total unsaturated hydrocarbons present 

 consisted of this compound. 



The presence of acetylene at the point where luminosity commenced 

 naturally suggested that it was in some way due to actions in which 

 the acetylene played the principal part either that it split up into 

 carbon and hydrogen under the influence of heat, and so supplied the 

 flame with the solid particles necessary, according to Sir Humphry 

 Davy's theory of the cause of luminosity, or else by its polymerisation 

 it formed the dense vapours required by Dr. E. Frankland's more 

 recent hypothesis. 



In order to elucidate this point, I carried out the long series of 

 experiments upon the action of heat upon flowing ethylene and other 

 hydrocarbons, which formed the subject of communications to the 

 Royal Society in 1893 and early this year, in which I showed thai- 

 whilst flowing through a heated area (the temperature of which was 

 between 800 and 1000 C.), ethylene decomposed according to the 

 equation 



and that the acetylene then polymerised into a large number of more 

 complex hydrocarbons, amongst which benzene and naphthalene were 

 conspicuous, whilst at temperatures above 1200 C., no polymerisation 



