BY 0. M. MITCHELL, A.M.,

DIRECTOR OF THE CINCINNATI OBSERVATORY.

NEW YORK:

OAKLEY & MASON,

21 MURRAY STREET.

1

Entered according to act of Congress, in the year 1848, by

0. M. MITCHEL,

In the Clerk's Office of the District Court of the United States for the Southern

District of Ohio.

PREFACE.

A FEW words ir explanation of the circumstances under which this volume is presented to the public, may not be unacceptable to the reader. It is now a little more than six years since the writer conceived the idea of erecting a great astronomical observatory in the city of Cincinnati. My attention had been for many years directed to this subject, by the duties of the professorship, which I then held in the college. In attempting to communicate the great truths of astronomy, there were no instruments at hand, to confirm and fix the wonderful facts recorded in the books. Up to that period our country, and the west particularly, had given but little attention to practical astronomy. A few individuals, with a zeal and ardor deserving of all praise, had struggled on to eminence almost without means or instruments. An isolated telescope was found here and there scattered through the country; but no regularly organized observatory with powerful instruments, existed within the limits of the United States, so far as I know.

To attempt the building of an observatory of the first class, and to furnish it with instruments of the highest order, without any aid from the general or state government, but by the voluntary contribution of all classes of citizens, was an enterprise of no common difficulty. To ascertain whether any interest could be excited in the public mind, in favor of astronomy, in the spring of 1842 a series of lectures was delivered

in the hall of the Cincinnati.College. To give an incre..sed effect to these discourses (which were unwritten, and in a style of great simplicity), a mechanical contrivance was prepared, by the aid of which the beautiful telescopic views in the heavens were presented to the audience, with a brilliancy and power scarcely inferior to that displayed by the most powerful telescopes. To this fortunate invention were these lectures, no doubt, principally indebted for the interest which they produced, and which occasioned them to be attended by a very large number of the intelligent persons in the city Encouraged by the large audiences, which continued through two months to fill the lecture-room, and still more by the request to repeat the last lecture of the course in one of the great churches of the city, I matured a plan for the building of an observatory, which it was resolved should be presented to the audience at the close of the lecture, in case circumstances should favor. Through the kindness of a few friends, who were now beginning to take a deep interest in the matter, more than two thousand persons were in attendance; and it seemed that the moment had arrived for taking the first step in an enterprise whose fate it was impossible to predict.

Having closed the subject under discussion, the audience were requested to give me a few minutes of time, for the explanation of a matter which it was hoped would not be received without some feelings of interest and approbation. The rapid advances of astronomy in Europe were then referred to the erection of observatories in all parts of the world—the variety of magnificent instruments in Russia and Germany, in France and England, and the utter deficiency of our own ountry in every thing pertaining to the science of the stars