250 ON THE LIGHT OF THE MOON AND OF THE PLANET JUPITER. 
The following are the observations made for the purpose of determining /,, the 
mean quantity of moonlight at the several phases; d represents the distance of the 
centre of the bulb from the diaphragm of the lamp. In these and in subsequent 
experiments, four Carcel lamps, distinguished by the letters J, R, S, and W, were used, 
with hollow cylindrical flames, the oil being supplied at the lower edge of the flame 
by clockwork. A few comparisons of Jupiter and Venus, taken at the same time, are 
included. | 
PHOTOMETRIC OBSERVATIONS UPON THE Moon, JUPITER, AND VENUS. 
1860, March 24th. Lamp S, diaphragm Z. “A few clouds near the horizon, but 
the sky seems perfectly clear in the intervals.” 
h ft. 
8 3 Sidereal time. Moon 24 days old. “A cloud not far off, 10° or 15° from Moon" d = 38.5 
8 4 « Di Di [11 [11 Di d = 38.5 
821 * = " “ Perfectly clear.” d = 36.0 
8 6 s Venus. a 0650 
8 10 « « | | d = 47.0 
8 23 KÉ e Se 47.0 
8 12 =e Jupiter. : : 3 d! = 93.5 
8 19 " " e : d'= 98.5 
8 26 s ei d'= 108.5 
The position of the lamp was thought rather too high, and was altered on the sub- 
sequent evenings; this, if at all sensible, would cause the Moon, Venus, and J upiter 
to appear too bright on the 24th. The equalization of the images was noted by two 
observers, the position of the bulb being frequently changed. The chief uncertainty 
arises from the red color of the flame when contrasted with the Moon and planets, 
though when seen by itself it looks quite white. The Moon was only about 8° above 
the horizon. 
March 25th. Lamp S, diaphragm Z. “Cleared suddenly. A pure sky, and the 
‘lumiére cendrée' unusually distinct.” 
A thin eloud was notieed just below the e 
: two when the observations were com- ? d — 10.6 
gien S in : S eer ie but it soon dispersed. 
8 8 & s D 
e 
7 94 Sid. time. Moon 33 days old, near Venus. 
a= 90 
d = 12.1 
