SCIENTIFIC SUMMARY. 
419 
one-2, 968, 300th of the sun’s mass, or approximately one- ^ - ^^^ th part of 
Leverrier’s estimate, say one-25th of the 3,000,000th part of the sun’s mass ; 
or, since the earth’s mass = one-350, 000th part of the sun’s, in round numbers, 
the reduction is equivalent to one-216th part of the earth’s mass. We may 
say roughly that our estimate of Mars’s mass must be diminished by one- 
200th part of the earth's mass, or by some 30 millions of millions of millions 
of tons. 
Spectra of Comets b and c, 1877. — The spectrum of Winnecke’s comet b 
1877, examined with a Browning single prism spectroscope, by Copeland 
and Lohse of Lord Lindsay’s observatory, was found to consist of three 
bright bands, closely resembling those of comet II., 1868, as figured by 
Dr. Huggins. The spectrum of comet c (Borelly’s) was found also to con- 
sist of three bright bands, but not coinciding with those of the other comet. 
They seem to correspond with those seen by Huggins in the spectrum of 
Brorsen’s comet of 1868, and comet I., 1871. The measures were all made 
with a spider line, or a steel cone, in either case feebly illuminated in an 
otherwise perfectly dark field. Lord Lindsay considers the steel cone the 
best, as it gives a broader line, and requires less illumination. 
Two Flats on the Moons Limb . — Dr. Ralph Copeland has recognized two 
remarkable “ flats” on the moon’s limb. The positive angles of their centres 
were found to be 264° 28' and 272° 30', their lengths being V 39"T and 
1' 18" -2 respectively. They coincided sensibly with a spider line through- 
out their entire length. Assuming the lowest points to have been exactly on 
the moon’s limb, these measures give the following results : — 
Length in arc of moon’s limb 
Apparent depth 
,, „ in feet, about 
Selenocentric latitude 
,, longitude . 
First Depression. 
Second Depression. 
. 5° 46' 
4°3P 
. l"-24 
0"-78 
. 7,200 
4,500 
. - 14° 25' 
- 6° V 
. +87 18 
+ 86-41 
It seems highly probable that these indentations are identical with two of 
those seen by Cooper Key on Sept. 6, 1863. Dr. Copeland, after comparing 
together various observations, comes to the conclusions that, — 
The first depression is most probably caused by the presence of the adjoin- 
ing ring-plains, Ansgarius and Lehaim, on the moon’s limb ; 
And that the second depression is undoubtedly a vertical section of 
Kastner. 
Collective Light and Distribution of the Fixed Stars. — Mr. J. J. Plummer has 
endeavoured to determine the total illuminating power of the stars as com- 
pared with acknowledged photometric standards. He finds that the total 
illuminating power of all the stars above the horizon at one time is not less 
than one-eightieth part of the illumination due to the full moon. In deal- 
ing with stars of lower magnitudes, he is led to the conclusion that either 
Argelander’s Durchmusterung contains many stars (more than one-third of 
the entire number) which, though rated as 9-5 magnitude, are sensibly 
below it, or else it must be assumed that at the average distance for stars of 
this magnitude a denser stratum actually exists, succeeded possibly by 
regions less fruitful beyond. u Having been led to the latter conclusion in 
