308 
d'autres issues du corps, qu’on regarde comme impures 
et souillées’’ (Pierre Gonnerat, ‘‘ Voyage aux Indes 
Orientales et 4 la Chine,” & Paris, 1782, vol. i., p. 93). 
Kumacusu Minakata. 
Tanabe, Kii, Japan, December 13, 1913. 
Systems of Rays on the Moon’s Surface. 
A Great deal has been said, and a great many 
theories have been put forward, as to the cause of 
these marvellous systems of rays on the surface of 
the moon. I now venture to put forward an explana- 
tion which has occurred to me, and should like the 
opinion of some of your readers upon it. 
It is generally admitted that the volcanic action of 
the moon was of an enormous character, ‘‘ even 
when the low force of lunar gravity is taken 
into consideration,” and from our knowledge 
of the amount of lava emitted from one _ of 
our own small craters, we can conceive what 
a huge volume must have been thrown out from such 
gigantic craters as Clavius, Ptolemaus, or Copernicus. 
Now, from what we can see even to-day, the lunar 
surface is exceedingly mountainous, and I suggest 
that when these craters were in their full power huge 
volumes of lava were thrown out, and in many cases 
practically filled up valleys, or cafons between the 
mountains. We know the rays are from five to ten 
miles broad, even up to twenty miles, and from the 
action of the volcano there would always be the 
tendency for the lava to run away from the crater 
itself, thus forming these rays, like spokes from a 
hub. Some of the rays are, however, apparently of 
a prodigious length, up to 2000 miles long, but Prof. 
Pickering tells us that this length is an illusion, the 
long rays being made up of rays from different 
craters, which appear to form one long continuous 
ray, which satisfies the question of length. 
Then many of these rays apparently run 
right across and almost obliterate (at full 
moon) such craters as Clavius and Maginnus. 
Now I think it is generally admitted that the ray 
systems from Tycho, Copernicus, and Kepler are the 
largest on the moon, and they are also three of the 
very largest craters. This points to the fact that they 
were the first eruptions on the lunar surface, and 
being the first, threw out the greatest volume of lava. 
This filled up the valleys in their neighbourhood, but 
afterwards other craters were erupted through the 
lava-covered rocks, though without breaking up the 
“lava valleys.” It is highly probable that in these 
circumstances most, or all, the craters have their rays, 
though too small to be detected through even the 
largest glass. Their brilliance would, of course, be 
accounted for, by the sun shining directly upon them, 
through no atmosphere at all, or none worth men- 
tioning. It seems, therefore, to me, that these rays 
must be geologically old remains of eruptions, dried 
up now, but still showing themselves on the lunar 
surface, though it is doubtful if the matter will ever 
be satisfactorily cleared up. C. Hupert Pranr. 
49 Lichfield Road, Walsall, December 16, 1913. 
THE CAPE OBSERVATORY. 
Ts the preface to this work Sir David Gill relates 
that when, as a young astronomer, he was 
connected with Lord Crawford in the design and 
erection of the observatory at Dun Echt, he 
turned for assistance to Wilhelm Struve’s “ De- 
scription de l’Observatoire Astronomique Central 
1 “A History and Description of the Royal Observatory, Cape of Good 
Hope." By Sir Mavid Gill K.C.B. F.R.S. Pp. cxe+136+plates, | 
(London: H.M. Stationery Office, 1913.) 
NO. 2307, VOL. 92] 
NATURE 
[JANUARY 15, I914 
de Poulkova.’”” Remembering the help and 
pleasure which Struve’s work"had given him, he 
resolved, in humble imitation, to write a descrip- 
tion of the Cape Observatory. 
“Struve,” in the words of Gill, “had the true 
genius and spirit of the practical astronomer, the 
love of refined and precise methods of observa- 
tion, and the inventive mechanical and engineer- 
ing capacity.” 
Struve had the rare opportunity of building an 
observatory after his own heart, regardless of 
expense, which should fulfil the highest require- 
ments of the astronomy of his time. Gill, 
animated by the same spirit as Struve, and with 
similar qualifications, greatly extended and re- 
modelled an historic observatory. Thanks to his 
grasp of the trend of astronomy, his skill in the 
design and construction of instruments, and his 
administrative ability and energy, he left the Cape 
Observatory, at the close of his directorate, one 
of the best equipped and most efficient observa- 
tories in the world. 
The volume, as its title indicates, is divided 
into two parts. The first consists of a history 
of the observatory from its foundation to the pre- 
sent time, with brief biographical notices of those 
who have filled the position of H.M. Astronomer, 
and an appreciative criticism of their work and 
their contribution to the development of the ob- 
servatory. Following this is a brief account of the 
past and present instrumental equipment, and a 
comprehensive survey of the important astro- 
nomical and geodetic results which have pro- 
ceeded from the Cape Observatory. The second 
part of the book is devoted to a detailed descrip- 
tion, illustrated by many photographs and 
diagrams, of the important instruments which 
have been erected at the observatory during Sir 
David Gill’s directorate. 
The value of the Cape as a site for the exten- 
sion of astronomy and geodesy to the southern 
hemisphere was first appreciated by Lacaille, who 
in a brief visit in the middle of the eighteenth 
century made observations of the positions of 
more than 10,000 stars, and measured an arc of 
the meridian. 
After the British occupation, the establishment 
of a permanent observatory at the Cape was con- 
sidered by the Board of Longitude in February, 
1820; the appointment of an astronomer was 
recommended, and estimates were obtained from 
Troughton, Dollond, and Jones for suitable equip- 
ment. The Board of Admiralty expressed its 
concurrence with this proposal, and the observa- 
tory was established by Order in Council on 
October 20, 1820, the staff to consist of one 
astronomer, one assistant, and one labourer. 
The Rey. Fearon Fallows, fellow of St. John’s 
College, Cambridge, was appointed H.M. Astro- 
nomer, and directed to make observations so far 
as possible similar to and complementary to those 
at Greenwich. He fixed the site of the observa- 
tory on part of a bare, rocky hill, covered with 
thistles and infested with snakes, but tolerably 
free from the sandy dust prevalent near Cape 
Town, and commanding a good view of Table 
