THIS volume, both in respect to matter and arrangement, is designed especially for the use of the cadets of the U. S. Military Academy, as a supplement to the course in General Astronomy at present taught them from the text-book of Professor 0. A. Young. It is therefore limited to that branch of Practical Astronomy which relates to Field Work, and more particularly to those subjects which are not discussed at sufficient length for practical work in Professor Young's volume. It is believed, however, that it will find a useful application in the hands of officers of the Army, who may be called upon to conduct such explorations and surveys for military purposes as the War Department may from time to time direct.

LEARNED mathematician of the seventeenth century, Ozanam by name, a member of the Academy of Sciences and author of several distinguished works, did not think it derogatory to his dignity to write, under the title of " Mathematical and Physical Recreations," a book designed for the amusement of youth, in which science lends itself to every pastime, even jugglery and tricks of legerdemain.

THE author has no other apology to present for offering to the public the following work on " Popular Astronomy " than the marked favour with which his " Orbs of Heaven " has been received, both in this country and in Europe.

THE large modern telescope, celestial photography, and improved astronomical instruments have opened the field of astronomy to such an extent that the ideas, statements, and figures of a few years ago are no longer authentic. Happily for the credit of astronomers, the wonders of the skies have been underestimated, and those who thought that statements that had been previously made regarding celestial wonders were almost beyond credence will be pleased to find that they were not only true, but that in reality not more than half the truth had been told.

NEGLECT hitherto of the availability of astronomy for a laboratory course has mainly led to the preparation of this New Astronomy. Written purely with a pedagogic purpose, insistence upon rightness of principles, no matter how simple, has everywhere been preferred to display of precision in result. To instance a single example : although the pupil's equipment be but a yardstick, a pinhole, and the l rule of three, 1 will he not reap greater benefit from measuring the sun for himself (page 259), than from learning mere detail of methods employed by astronomers in accurately measuring that luminary ?...

I HAVE written these pages, not for the professional reader, but with the hope of reaching a part of that educated public on whose support he is so often dependent for the means of extending the boundaries of knowledge.

It is not generally understood that among us not only the support of the Government, but with scarcely an exception every new private benefaction, is devoted to " the Old " Astronomy, which is relatively munificently endowed already ; while that which I have here called "the New," so fruitful in results of interest and importance, struggles almost unaided.

IN the present edition the Author has adapted the rules not only to the Tables of Dr. Inman (the most comprehensive and useful yet published), but also to those in more general use, such as Riddle's, Norie's, &c. The student will therefore find now no difficulty in working out the examples contained in the book by any of the above tables, In the last edition of the Author's work on Plane and Spherical Trigonometry, rules are also given depending on the common tables of sines, &c,, as well as on the table of haversines contained in Inman's Tables.