g8 Count Rumford's Account of a Method of 
in one experiment, appeared to be ,4816 parts ; and with 
another looking-glass it was ,4548 parts in one experiment, and 
,4430 in another. I should certainly have made an experi- 
ment to determine the loss of light in its reflection from the 
surface of a plane metallic mirror, but I had no such mirror 
at hand. 
The difference of the angles of incidence at the surface of 
the mirror, within the limits mentioned, namely, from 45 ^ 
85°, did not appear to affect, in any sensible degree, the re- 
sults of the experiments. I also found upon trial, that the ef- 
fect produced by the difference of the angles at which light 
impinges against a sheet of transparent glass through which it 
passes, is, within the limits of 40° or 50° from the perpendicu- 
lar, but very trifling. 
Of the relative Quantities of Oil consumed, and of Light emitted, 
by an Argand's Lamp , and by a Lamp on the common Con- 
struction, with a Riband Wick. 
The brilliancy of the Argand’s lamp is not only unrivalled, 
but the invention is in the highest degree ingenious, and the 
instrument useful for many purposes; but still, to judge of its 
real merits as an illuminator, it was necessary to know whe- 
ther it gives more light than another lamp in proportion to 
the oil consumed. This point I determined in the following 
manner. 
Having placed an Argand's lamp, well trimmed, and 
burning with its greatest brilliancy, before my photometer, 
and over against it a very excellent common lamp, with a 
riband wick, about an inch wide, and which burnt with a 
