254 ON THE LIGHT OF THE MOON AND OF THE PLANET JUPITER. 
h . ft. 
13 49 Sid. time. Moon 8 days old. Lamp S. Diaphragm X. In open air. d — 85 
D DI “ Di d = 40 
D “ Di & d = 41 
14 14 4 = e With screen. d — 490 
« se se « d — 4.60 
e e ; z S d = 4:15 
14 19 E M X e " d = 48 
Di Di & Di d — 47 
Di Di a u & d — 4.8 
June 2d. Perfectly clear. 
h ft. 
17 40 Sid. time. Moon half a day from full. Lamp S. Diaphragm X. With screen. d = 2.20 
$ a E e - d — 92.40 
T = « e - d = 2.30 
June 12th. Clear. 
hm A : ft. 
14 15 Sid. time. Venus. Lamp S. Diaphragm X. With sereen. d' — 63.8 
z a s v... = 658 
In the reductions, we must allow for the proportion of light extinguished by the 
atmosphere, taking the light when the object is in the zenith as a standard. To do 
this, the light as observed must be multiplied by a coefficient e, the numerical values of 
which have been adopted from Seidel. These must be applied, together with the coeffi- 
cient y, as mentioned in the notes appended to the observations on March 30th, April 
2d, and May 28th. The comparisons made with other apertures, as with X, or with 
the whole flames, must be reduced, as directed in the notes. The amount of illu- 
mination afforded by the aperture Z at the axis of the pencil, is considered to be con- 
stant at the same distance. 
The object of the investigation, as respects the Moon, is to find H. by applying the 
formula (28). The observations upon Jupiter and Venus are not numerous enough to 
exhibit the variations of phase, but will furnish normal values of di and dj", by means 
of which their light may be compared with moonlight. 
Let 
d, = The distance in feet from the aperture Z, at which the illumination from the lamp is equal to that 
received from the standard phase of the Moon. 
The corresponding distance for Venus. 
d," — The corresponding distance for Jupiter. 
a 
ll 
