230 Dr Fyfe on the IMuminating Power of Coal-Gas, &c. 
Composite, 1s. 1d. per pound lasts for eight hours, expense 
8.6 farthings, light 1 to 3, expense 8 to 1. 
Diaphane (French), 1. 8d., will last 6.6 hours, at a cost of 
13.3 farthings, light 1 to 3, expense 15.1 to 1. 
Margerine, nearly in every respect the same as diaphane. 
Spermaceti, 2s. 6d. per pound, will burn for eight hours, cost 
20 farthings, light 1 to 2.6, expense as 16.2 to 1. 
Composition candle the same. 
Wax 2s. 6d., burns nine hours, cost 20 farthings, light as 1 to 
2.6, expense therefore as 14.4 to 1. 
Thus the ¢a//ows, with the exception of the palm, are nearly 
of the same comparative expense, light for light ; the composi- 
tion is a very little more expensive, the others are more than 
double the expense. 
In the foregoing calculations, I have supposed the gas to be 
consumed by jets; but I have already shewn in the paper read 
before the Society, and published in its Transactions for 1840, 
that this is the least profitable method of burning it. For egua/ 
consumpts, the light given by other burners is much greater ; 
thus taking the jet as 100, that from a fish-tail is 140, from 
the bat-wing 160, and from a properly constructed argand 180. 
Accordingly, by consuming the gas with these, the compara- 
tive expense will be still farther reduced. The following table 
gives the comparative light and expense according to the kind 
of burner used. 
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