88 Count Rumford’s Account of a Method of 
the limits of the inconsiderable distances at which the candles 
were-placed from the photometer, in that case the distance of 
the two equal lights united ought to be to the distance of one 
of them single, in a ratio less than that of the square root of 2 
to the square root of 1. For if the intensity ot a light emitted 
by a luminous body, in a space void of all resistance , be dimi- 
nished in the proportion of the squares of the distances, it must 
of necessity be diminished in a still higner ratio when the light 
passes through a resisting medium, or one which is not per- 
fectly transparent : and from the difference of those ratios, 
namely, that of the squares of the distances, and that other 
higher ratio found by the experiment, the resistance of the 
medium might be ascertained. This I nave taken much pains 
to do with respect to air, but have not as yet succeeded in these 
endeavours, the transparency of air being so great that the 
diminution which light suffers in passing through a few inches, 
or even through several feet of it, is not sensible. 
Having found, upon repeated trials, that the light of a lamp, 
properly trimmed, is incomparably more equal than that of a 
candle, whose wick continually growing longer renders its 
light extremely fluctuating, I substituted lamps to candles in 
these experiments, and made such other variations in the 
manner of conducting them, as I thought bid fair to lead to a 
discovery of the resistance of the air to light, were it possible to 
render that resistance sensible within the confined limits of 
my machinery. 
Having provided two lamps, the one an Argand's lamp, 
which I made to burn with the greatest possible brilliancy ; 
the other a small common lamp, with a single, round, and 
very small wick, which burning with a very clear, steady flame, 
