376 Dr Fyfe on the Illuminating Power of Coal and Oil Gas . 
equal to that of 4*24 candles per foot. No. 1. (Glasgow) con- 
sumed 1.36 foot, the light being equal to 5. 95 candles ; and 
No. 2, consumed 2 feet, the light being that of 5.64 candles. 
It appears, then, that the light afforded by the consumpt of 
equal quantities of gas, depends much on the size of the burner. 
The burners No. 2. seem to be better than No. 1. ; but it would 
require an extensive series of experiments on this subject before 
any satisfactory conclusions can be drawn ; and I conceive it is 
a subject well worthy the serious consideration of oil-gas and 
coal-gas establishments. 
Note.-— Since most of the preceding experiments were per- 
formed, a letter has appeared from Professor Leslie to the Coal- 
Gas Company, in which the illuminating power of the gases is 
stated at 1 to 1.5, rather less than the average conclusion at 
which I have arrived. Of the accuracy of the mode of judging 
of the intensity of the light I cannot speak, not being acquainted 
with the method adopted for preventing any irregular action of 
heat on the photometer ; but, allowing it to be a correct one, 
let us try if we can account for the discordance in the results. 
In drawing my conclusion, I have fixed on the gas containing 
32 per cent, of olefiant gas, compared to the coal-gas as having 
15 and 17 ; and hence I make the illuminating power as 1 to 2, 
and as 1 to 1.8. It has been already stated, that the gas lately 
made by Mr Milne is of inferior quality, owing to his appara- 
tus being out of repair, in which state, I am informed, it has 
been for some time past. Suppose, then, that the gas given to 
Professor Leslie was similar to that on which some of my expe- 
riments were performed, and which contained 25 olefiant gas, 
while the coal-gas contained 15, the illuminating power should 
be as 1 to 1.6 ; if the latter had 17, it would be as 1 to 1.47; 
both of which results very nearly agree with those of the Pro- 
fessor, 
