measuring the comparative Intensities of Light. 91 
mind might be totally unbiassed by my expectations, or by any 
opinions I might previously have formed with respect to the 
probable issue of the various experiments, keeping my eye 
constantly fixed upon the field of the photometer, and causing 
the light, whose corresponding shadow was to be brought to 
be of equal density with the standard, to move backwards and 
forwards, by means of the winch which I had constantly in 
my hand, as soon as the shadows appeared to me to be per- 
fectly equal, I gave notice to an assistant to observe, and si- 
lently to write down, the distance of the lamp or candle, so 
that I did not even know what that distance was till the expe- 
. riment was ended, and till it was too late to attempt to correct 
any supposed errors of my eyes by my wishes, or by my ex- 
pectations, had I been weak enough to have had a wish in a 
matter of this kind. I do not know that any predilection I 
might have had for any favourite theory , would have been able 
to have operated so strongly upon my mind, and upon my 
senses, as to have made black and white appear to me other- 
wise than as they really were ; but this I know, that I was very 
glad to find means to avoid being led into temptation. 
But to return to the foregoing experiments ; the results of 
them, so far from affording means for ascertaining the resist- 
ance of the air to light, do not even indicate any resistance 
at all ; on the contrary, it might almost be inferred from some 
of them, that the intensity of the light emitted by a luminous 
body in air is diminished in a ratio less than that of the squares 
of the distances ; but as such a conclusion would involve an 
evident absurdity, namely that, light moving in air, its abso- 
lute quantity instead of being diminished actually goes on to 
increase , that conclusion can by no means be admitted. 
N 2 
