from the value of the map for handy reference in the usually dim light of
the observatory, without adding to its utility in other ways. Every named
formation is prominently shown; and most other features of interest,
including the principal rill-systems, are represented, though, as regards
these, no attempt is made to indicate all their manifold details and
ramifications, which, to do effectually, would in very many instances
require a map on a much larger scale than any that has yet appeared.

The insertion of meridian lines and parallels of latitude at every ten
degrees, and the substitution of names for reference numbers, will add to
the usefulness of the map.

With respect to the text, a large proportion of the objects in the
Catalogue and in the Appendix have been observed and drawn by the author
many times during the last thirty years, and described in _The
Observatory_ and other publications. He has had, besides, the advantage
of consulting excellent sketches by Mr W.H. MAW, F.R.A.S., Dr. SHELDON,
F.R.A.S., Mr. A. MEE, F.R.A.S., Mr. G.P. HALLOWES, F.R.A.S., Dr. SMART,
F.R.A.S., Mr. T. GORDON, F.R.A.S., Mr. G.T. DAVIS, Herr BRENNER, Herr
KRIEGER, Mr. H. CORDER, and other members of the British Astronomical
Association. Through the courtesy of Professor HOLDEN, Director of the
Lick Observatory, and M. PRINZ, of the Royal Observatory of Brussels,
many beautiful photographs and direct photographic enlargements have been
available, as have also the exquisite heliogravures received by the
author from Dr. L. WEINEK, Director of the Imperial Observatory of
Prague, and the admirable examples of the photographic work of MM. PAUL
and PROSPER HENRY of the Paris Observatory, which are occasionally
published in _Knowledge_. The numerous representations of lunar objects
which have appeared from time to time in that storehouse of astronomical
information, _The English Mechanic_, and the invaluable notes in