372 Dr Fyfe on the Illuminating Power of Coal and Oil Gas. 
The gases used in these trials contained the one 15, the other 
25 of olefiant, making the illuminating power, by this method, 
as 1 to 1.66. 
I have stated, that the light given by a burner consuming 
one cubic foot of good oil-gas per hour, has been found by Mr 
Milne, when it was burnt under favourable circumstances, to 
be equal to that of eight candles (short sixes). In the experi- 
ments just detailed, the average does not amount to above 6, 
and even in that giving the most light it is only 7.8 ; so that the 
gas used must have been of rather inferior quality. Mr Milne 
accounts for it, by his apparatus being at present not in good 
repair. Suppose we take gas giving a light equal to that of 
eight candles, and bring it in opposition to the Edinburgh coal- 
gas, their illuminating power is, taking the coal-gas at the 
highest, as 6.6 to 8, that is, as 1 to 1.12 ; and taking it at the 
lowest, as 3.84 to 8, or as 1 to 2.09. But taking the coal-gas at 
the average of all the preceding trials, which is 4.69, then the 
illuminating power is as 4.69 to 8, or as 1 to 1.7. 
From what has now been said, we are still more enabled to 
judge of the accuracy of the method proposed for ascertaining 
the illuminating power. By the trials mentioned, it is 
By the Consumpt. By the Chlorine Test, 
as 1 to 1.9 as 1 to 1.8 
1 to 1.8 1 to 1,6 
1 to 1.4 1 to 1.6 
1 to 1.35 1 to 1.36 
varying in its results only from 0.1 to 0.2 from those given by 
the other mode. 
In having recourse to this test, we are saved the trouble of 
measuring the consumpt of the gases, and avoid also the un- 
certainty as to the intensity of the shadow, for unless we are ac- 
curate in this, it is impossible to ascertain, with any degree of 
certainty, the power of giving light. It possesses another ad- 
vantage, that of finding the illuminating power of gases in dif- 
ferent places. If, therefore, it should be adopted, it will be ne- 
cessary, with a view of avoiding confusion, to fix on some point 
to commence with, and call the lighting power at this 1. Per- 
haps it will be best to state it just as the quantity of olefiant gas, 
that is, if the gas contains 15 per cent., let its illuminating 
power be termed 15, and so on, according to the proportion. 
