8. REPORT—1868. 
For season :— O—8 =133 40-4. 
Lunar summer in the northern hemisphere. 
For position :—N. and §., Moon’s latitude = 4 54:88. 
EK. and W., Moon past perigee 200 hours. 
Moon less apogee 150 hours. 
Objects are south and east of their mean places. 
For size :—Moon’s semidiameter 15’ 12-9; mean semidiameter 15’ 32:3. 
A circle of one degree in diameter at the centre of the moon’s disk is seen 
under an angle of 16":277; at 5° of longitude W. or E. the degree is fore- 
shortened in a radial direction, z.¢. on the equator by 0”:061, the shortest 
diameter being 16-216. At 10°, the N.W. angle of area IV A®, or N.E. of 
III A&, the foreshortening amounts to 0'"247, or nearly a quarter of a second, 
the shortest diameter being 16'030. 
The number of English feet subtending an angle of 1':0 at the centre of the 
moon’s disk at mean distance is 6116-7. This value is increased in receding 
from the centre in the proportion of the secants of the angular distances from 
the centre ; consequently at the middle point of each area the value of 1-0 is 
greater than at the centre of the moon’s disk ; for, by reason of the spherical 
surface of the moon, 1:0 covers a greater portion of the surface at a point 
removed from the centre than at the centre. At the middle point of IV A‘, 
or 2° 30' W. long., 2° 30'S. lat., the angular distance from the centre=3° 32’, 
which gives 6128°3 English feet for the value of 1-0. At the middle point 
of IV A’, or 7°30’ W. long., 2° 30'S. lat., the angular distance from the centre 
=7° 54’, which gives 6175°3 English feet for the value of 1-0. This is also 
the value for the middle point of IV A’. At the middle of IV A”, or 7° 30’ 
W. long., 7° 30’ S. lat., the angular distance from the centre=10° 35’, which 
gives 6222-7 English feet for the value of 1':0. 
While the values of 1'0 vary in the proportion of the secants as we recede 
from the centre of the disk, the objects themselves remain of the same extent, 
and are seen at mean libration, either under the larger angle produced by the 
moon passing her perigean point, or under the smaller as she passes her apo- 
gee. Taking 6116-7 as a standard quantity, expressing the diameter of a 
circle seen under an angle of 1:0 at mean distance, this quantity is seen at 
the centre of the disk, mean libration, moon in perigee, under an angle of 
1-059 +, moon in apogee 0-941. At perigee, mean libration, at the middle 
point of IV A*, the foreshortening of an object of this extent is given by the 
following numbers :—Longest diameter 1”:059, shortest 1-057. The differ- 
ence is perfectly inappreciable ; it is therefore presumable that we see very 
nearly the true forms of the objects on this area. At apogee, mean libration, 
the proportions are—0":941 longest diameter, 0':939 shortest. For the 
middle points of TV Af and IV A¢ we have:—longest diameter 1-059, shortest 
1-049, moon in perigee ; and 0-941 longest diameter, 0-932 shortest, moon 
in apogee. At the middle point of IV A” the foreshortening is greater, but 
still small :—moon in perigee, longest diameter 1-059, shortest 1-041 ; moon 
in apogee, longest diameter 0'°941, shortest 0-925. 
All the objects situated in areas IV A* and IV A® are so affected by libration 
that we see alternately more or less of their N. and §. sides. From the ele- 
ments of Rutherford’s photogram already given, it is easy to perceive that 
although the places are laid down on the areas for mean libration, the N. sides ) 
of the objects are presented in that photogram more directly to the eye; and 
this will to some extent affect the outline, inasmuch as the measures, more 
