PT^HE remarks which appear in the Preface to the Third Edition (see post] apply almost word for word, so far as they go, to the Fourth Edition. Yet it is necessary for me to write an independent Preface in order to call attention to the altered circumstances under which this work is now presented to the reader. If the development of Astronomy between 1867 and 1877 was great, its development between 1877 and 1889 has been still greater. And besides this, there were important omissions in the ground-plan of the book which I have long been very desirous of making good, whenever time or opportunity became available.

THERE is bat little alteration in this edition, for so far as regards the older astronomers at all events there has been nothing to add or to correct. It may, however, be mentioned here that a commemorative tablet has recently been placed on the house, in New King Street, Bath, in which William Herschel resided. Nor could it be possible to allow the sketch of the late Earl of Eosse to be reprinted without adding the fact that his youngest son, Hon. C. A. Parsons, is, as all the world knows, the famous engineer who invented the steam turbine.

THE rapid progress of the science of astronomy, for the liwr. "few years, has again rendered it necessary to revise the Geography of the Heavens a work, the popularity of which is sufficiently proved by a sale of 300,000 copies. The editor has, therefore, availed himself of the occasion to make such improvements, both in the book and maps, as seemed to be demanded by the progress of the science, and the most approved methods of instruction.

In this work the Author has endeavoured to cover as wide a field as possible and it has necessarily been somewhat difficult to decide upon what to include and what to omit, especially when dealing with the most recent developments. It is hoped, however, that the book will serve to give the reader a sufficiently complete view of the present state of Astronomy.

DURING the past few years great advances have been made in astronomical science. A new horizontal parallax of the sun has been established. This has materially altered the estimated distances, etc., of the planets. The sun is much nearer us than we supposed, and light has lost a little of its wonderful velocity. , Much additional information has been obtained concerning Meteors and Shooting Stars. The investigations connected with Spectrum Analysis have been especially suggestive.

THIS small volume is not offered to the public as an original treatise upon its subject. It is merely a brief compilation of the facts of Astronomy, as presented by the acknowledged authorities, together with some slight reference to various theories not yet substantiated.

MY experience in presenting the elements of practical astronomy to rather large classes of students in the University of Michigan led me to the conclusion that the extensive treatises on the subject could not be used satisfactorily, except in special cases. Brief lecture notes were employed in preference. Arrangements were made with a local publisher that the notes should be written out in full and printed, almost exclusively it was supposed, for use in my own classes. The process of enlargement had just begun when the call to my present position was accepted.

The author feels that critical examination of this monograph may show in many points a want of consistency and continuity. The ground covered is so extensive, the material so diverse as well as voluminous, and the relations to be investigated so numerous, that no conclusion could be reached on one point which was not liable to be modified by subsequent decisions upon other points. The author trusts that the difficulties growing out of these features of the work, as well as those incident to the administration of an office not especially organized for the work, will afford a sufficient apology for any defects that may be noticed.

NAUTICAL ALMANAC OFFICE, U. 8. Naval Observatory, January 7, 1895.