THIS work is designed to meet the special requirements of officers of the Merchant Service, and to be a complete Text-; Book on Navigation, etc., for the general student.

THE present work is not a compendium of astronomy or an outline course of popular reading in that science. It has been prepared as a text-book, and the author has purposely omitted from it much matter interesting as well as important to a complete view of the science, and has endeavored to concentrate attention upon those parts of the subject that possess special educational value. From this point of view matter which permits of experimental treatment with simple apparatus is of peculiar value and is given a prominence in the text beyond its just due in a well-balanced exposition of the elements of astronomy, while topics, such as the results of spectrum analysis, which depend upon elaborate apparatus, are in the experimental part of the work accorded much less space than their intrinsic importance would justify.

THE author has embraced the opportunity afforded by a second edition of this work to introduce into it certain changes which, without modifying the general plan and scope, will, it is hoped, increase its usefulness. For the most part these changes are made in the direction of increased simplicity or of increased precision, and are most conspicuously shown in 19, 23, 3,2, 37 and 38. The tables at the end of the book have been considerably increased, both in extent and precision, and now suffice for approximate as well as rough determinations of time, latitude and azimuth without the use of an almanac.

THE following treatise was undertaken at the suggestion of some friends, and in a persuasion, that a classic of the kind was necessary in our institutions of learning. The larger works on astronomy seemed too unwieldly for common use. Much of Mr. Ferguson's original work had become obsolete ; and it may now be considered as defective, for want of the great improvements of Herschel and his cotemporaries. Though Dr.Brewster may have supplied the deficiency, he has retained much of the obsolete part, and his work is too expensive for admission into most of our seminaries. The latter objection applies with equal force to Enfield, and some others. Most of the smaller works on astronomy had not been published, or were not known to the author of this, when it was commenced. Though the public are now favored with several compends on astronomy, none of them seem calculated for that class of students, for which this was intended.

MOST of the articles in the following pages have been published during the last few years in The Gentleman's Magazine, Knowledge, The Observatory, etc., and my thanks are due to the editors and publishers of these periodicals for permission to re-publish them. The articles have been carefully revised and partly re- written, and the information brought up to date. The following articles have not been previously published, " The Ring Nebula in Lyra," "The New Star in Perseus," and "The Coming Comet." For the illustrations my best thanks are due to Professor Barnard, D.Sc. of the Yerkes Observatory (U.S.A.), M. Henry, of the Paris Observatory, and Dr. W. E. Wilson, F.R.S.

IN presenting the subject of Astronomy at Teachers' Institutes and similar gatherings, I have frequently been requested to recommend a handbook for ready reference by which one pursuing the subject without a teacher might not only learn the general facts of Astronomy, but also trace out the constellations and learn the mythological stories in connection with them. I know of several excellent books on the subject, but none containing this last-named feature and I decided to write one. I stated this fact to a Teachers' Institute (in Montgomery Co., Pa.), and stated also that, owing to other work in hand, I could not do this within a year, whereupon the teachers to the number of three hundred and forty-two sent in their names as advance subscribers, if I would prepare the book immediately. This request could not be ignored, and hence this booklet is issued a year sooner than intended by the writer.

During my connection with the University of Michigan as Professor of Astronomy I felt very much the want of a book written in the English language, to which I might refer the students attending my lectures, and it seems that the same want was felt by other Professors, as I heard very frequently the wish expressed, that I should publish an English Edition of my Spherical Astronomy, and thus relieve this want at least for one important branch of Astronomy. How ever while I was in America I never found leisure to undertake this translation, although the arrangements for it were made with the Publishers already at the time of the publication of the Second German Edition.

IN preparing and issuing this collection of essays and addresses, the author has yielded to what he could not but regard as the too flattering judgment of the publishers. Having done this, it became incumbent to do what he could to justify their good opinion by revising the material and bringing it up to date. Interest rather than unity of thought has determined the selection.