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ticularly, on account of the disagreeable consequences to 
society, which always result from tedious and endless dis¬ 
putes. 
To perceive all the importance of the question we have 
agitated, we have only to consider the great advantage to 
the public, which cannot fail to result from the discovery of 
a fixed principle, which may be employed with facility and 
success, to perfect the art of illumination , and the instru¬ 
ments employed in it. 
What enormous sums are annually and daily expended to 
dissipate the darkness of night! and, moreover, in what a 
deplorable state do we find the science which ought to illus¬ 
trate all the details of this important operation ! 
How shall we attempt to perfect the art of illumination 
while we continue so ignorant of the nature of light, that 
we know not, even where to search for it ? 
Having considered this interesting subject for a long 
time, I have made a number of experiments which appear 
to me calculated to throw light on it. I am about to sub¬ 
mit them to the class, but it will be necessary to commence 
by premising a few words on a small change which I made 
on an apparatus already known, and of which I availed my¬ 
self in measuring the intensity of light. 
Instead of employing the rules divided into inches and 
tenths of inches, to measure the distances of lights on the 
photometer, I used rules divided into degrees, which indi¬ 
cated directly, and without any calculation, the relative in¬ 
tensities of the two lights which are compared together. 
These two rules, which are each twelve feet long, are 
divided in a similar manner. The first division of this kind 
of scale of light , which is on one of the extremities of the 
rules, is marked 10 degrees, and corresponds to ten inches 
of the middle of the vertical bottom of the photometer, 
when the rule is adjusted. The division which is marked 
100 degrees, is at the distance of 21.62 inches from the first, 
(that of i0°) or at 31,62 inches from the centre of the pho- 
