218 ON THE LIGHT OF THE MOON AND OF THE PLANET JUPITER. 
As this was considered the most satisfactory of the trials made with the colored 
screens, the corrections which have been applied in the reductions are here added. 
The intensity of the light of the two objects admitted by the focus diaphragm of 
07.0425 diameter, was judged to be the same when the ratio of the exposed areas of 
the object-glass was 
Area of object-glass for house — 0.090. 
Area of object-glass for Jupiter 
The actual illumination of the side of the house by the direct light of the Sun at an 
incidence angle of 30°, added to the light received by reflection from surrounding ob- 
jects, was estimated, experimentally, to be to the illumination which it would receive 
directly from the Sun, at perpendicular incidence, as 4 to 3; and the coefficient 2 has 
been accordingly applied to the ratio of the areas of the object-glass, so as to refer the 
comparisons to the maximum illumination of the object by direct sunlight. 
For distinct vision of the house, the eye-piece, with the focus diaphragm, was moved ` 
4".4 from the object-glass, contracting the angle subtended by the diaphragm at the 
i S ? : 270.0 1 ; : 
object-glass in the proportion 5744 = me: The coefficient for the correction of 
the light of Jupiter for phase is 1.016. The altitude of Jupiter was 67°, and that 
of the Sun 45°. We must apply the coefficient m to reduce the light of the 
planet for atmospheric extinction to the altitude of 45°. . The ratio of the intensity of 
sunlight at the Earth and Jupiter is 7 a Ot The average brightness of the whole 
disc of Jupiter is less than that of the part included within the diaphragm, in the 
proportion 1: 1.23. Lastly, the central element of Jupiter, which receives sunlight at 
perpendicular incidence, is brighter than the average of its disc in the proportion 
1.43 : 1. 
We then have 
3 1 1 d ; 
X =~ ITSE 1.016 eg ven . er E DH 
0.090 x 1 $e 1018 016 x 1.045 x 193 X 148 X 27.7 2.1; 
and therefore 
Albedo of white house 1 
— 
MA 
Albedo of Jupiter 2 
1 
The experiments were continued, and varied in the following way. The daylight 
was excluded from the dome, leaving only the object-glass exposed. The telescope 
being directed upon the object, the eye-piece lenses were removed, the focus diaphragm 
only remaining. The pencil of light admitted by the aperture in the diaphragm was 
then compared with the standard lamps, by equalizing the images of the two reflected 
