olonel Morris, R.E., under the direction of
Sir David Gill.[909] Bechuanaland and Rhodesia were subsequently
included in the work; and the Royal Astronomer obtained, in 1900, the
support of the International Geodetic Association for its extension to
the mouth of the Nile. Nor was this the limit of his design. By carrying
the survey along the Levantine coast, connection can be established with
Struve's system, and the magnificent amplitude of 105 deg. will be given
to the conjoined African and European arcs. Meantime, the French have
undertaken the remeasurement of Bouguer's Peruvian arc, and a
corresponding Russo-Swedish[910] enterprise is progressing in
Spitzbergen; so that abundant materials will ere long be provided for
fresh investigations of the shape and size of our planet. The smallness
of the outstanding uncertainty can be judged of by comparing J. B.
Listing's[911] with General Clarke's[912] results, published in the same
year (1878). Listing stated the dimensions of the terrestrial spheroid
as follows: Equatorial radius = 3,960 miles; polar radius = 3,947 miles;
ellipticity = 1/288.5. Clarke's corresponding figures were: 3,963 and
3,950 miles, giving an ellipticity of 1/293.5. The value of the latter
fraction at present generally adopted is 1/292; that is to say, the
thickness of the protuberant equatorial ring is held to be 1/292 of the
equatorial radius. From astronomical considerations, it is true, Newcomb
estimated the ratio at 1/308;[913] but for obtaining this particular
datum, geodetical methods are unquestionably to be preferred.

* * * * *

The moon possesses for us a unique interest. She in all probability
shared the origin of the earth; she perhaps prefigures its decay. She is
at present its minister and companion. Her existence, so far as we can
see, serves no other purpose than to illuminate the darkness of
terrestrial nights, and to measure, by swiftly-recurring and conspicuous
changes of aspect, the long span of terrestrial time. Inquiries
stimulated by visible dependence, and aided by relatively close
vicinity, have resulted in a wonderfully minute acquaintance with the
features of the single lunar hemisphere open to our inspection.

Selenography, in the modern sense, is little more than a hundred years
old. It originated with the publication in 1791 of Schroeter's
_Selenotopographische Fragmente_.[914] Not but that the lunar surface
had already been diligently