j6 Count Rumford's Account of a Method of 
of objects capable of acting upon the mind, and particularly 
by removing all straight lines and angles, and all unnecessary 
varieties of lights and shades, the attention might be concen- 
trated and fixed in such a manner as to render the sense of 
sight peculiarly acute in distinguishing any difference in the 
simple objects presented to the eye. But however plausible 
this reasoning may appear, I own the experiment did not an- 
swer my expectation. It is true, the apparent densities of two 
equal hemispheres of shade, in contact with each other, may 
be compared with great facility, and when no discernible dif- 
ference is to be perceived between them, it is more than pro- 
bable that they are in fact very nearly equal ; but still I have 
found by experience, that two equal parallelograms of shade in 
contact with each other may be compared with the same ease, 
and, I have reason to think, with equal certainty, and that 
even when these united shadows are bounded on three sides by 
a perfectly white surface, illuminated by the direct rays of two 
strong lights ; that is to say, when the screen with the qua- 
drangular opening or field is made use of. 
In describing the cylinders by which the shadows are pio- 
jected, I said they were fixed in the bottom of the box ; but as 
the diameters of the shadows of the cylinders vary in some 
small degree, in proportion as the lights are broader or nar- 
rower, and as they are brought nearer to or removed farther 
from the photometer, in order to be able in all cases to bring 
these shadows to be of the same diameter, which I have found 
by experience to be advantageous, in order to judge with greater 
facility and certainty when the shadows are of the same density, 
I have rendered the cylinders moveable about their axes^ and 
have added to each a vertical wing of an inch wide, ^ of 
