145 
Mr. Ritchie on a new photometer^ &c. 
out by the sun, and that afforded by a common candle, place 
one end of the instrument opposite the sun, and bring the 
candle opposite the other end, till the fluid in the stem remain 
stationary at the original division, and the light given out by 
the candle, will evidently be to that given out by the sun, as 
the square of a few inches to the square of the number of 
inches contained in 95,000,000 miles, provided none of the 
sun's light had been absorbed in its passage through the at- 
mosphere. The delicacy of the instrument is such, that if it 
be placed opposite the sun without a counteracting force, the 
light absorbed from the body will be so great as to cause 
the liquid to move through a tube 20 or 30 feet long. By 
covering one end of the instrument, and directing the other 
to various quarters of the sky, we can ascertain the relation 
between the quantities of light reflected from the atmo- 
phere, and clouds floating in those regions. 
I am just now constructing a photometer about two feet 
in diameter, and two or three inches deep, with which I 
liope to appreciate the effect of heat in the feeble rays of 
the moon. 
7. Though this instrument has some resemblance to Pro- 
fessor Leslie’s photometer, yet it is founded on principles 
essentially different. The one depending on the difference of 
the temperatures of the two bulbs, whilst the perfection of 
the other results from the equality of the temperature of the 
air contained in both chambers. The one has a scale a few 
inches long attached to one branch of the bent tube, whilst 
the scale of the other is the distance between the two anta- 
gonist flames. The delicacy of the one is, from its very 
MDCCCXXV. U 
