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his own language, before all the troubles (I will not call them difficulties) are overcome. And perhaps one of the most valuable results to be derived from a truly intellectual study of Astronomy is, the habit of keeping up a sustained attention to all the successive steps of a long series of reasonings. Power, and with it dignity, are gained to the mind by this noble exercise.

      To those who will venture upon the study of the science in this connected way, I can promise an ample and immediate reward. It is not simply that a clear understanding is acquired of the movements of the great bodies which we regard as the system of the world, but it is that we are introduced to a perception of laws governing the motion of all matter, from the finest particle of dust to the largest planet or sun, with a degree of uniformity and constancy, which otherwise we could hardly have ​conceived. Astronomy is pre-eminently the science of order.

      The immediate object of my Lectures would be obtained, if they should be found to offer some facilities to those who, acting under the inducements to which I have alluded, may endeavour to obtain a connected and accurate view of the principles of Astronomy. But I should think myself highly rewarded if I could believe that the insight into principles thus obtained, would induce any one to enter carefully into its details.

G. B. AIRY.

       Table of Contents

       Royal Observatory, Greenwich.

      1 ↑ These Lectures were originally delivered at Ipswich, on Monday evening, March 13th, 1848, and the five following evenings.

      ​

POPULAR ASTRONOMY.

      LECTURE 1.

       Table of Contents

      Evidence for the apparent Rotation of the Heavens round the Earth.—The Equatoreal.—Refraction.—The Transit Instrument.—The Mural Circle.—Mode of Observing.

BEFORE entering upon the subject of my proposed course of Lectures,^[1] it may perhaps be desirable that I should state, in as brief terms as possible, the views which have induced me to deliver them to the members of this Institution. When it was intimated to me that the offer of the course would be desirable, and when I felt that my compliance would show my good will to the Museum, I could not help thinking in the first place, that I should be in some slight degree departing from the intentions and objects of the Institution, though in the next place, I was certainly inclined to the opinion that such departure would be more imaginary than real. I thought that lectures on Natural Philosophy would seem to be hardly proper in an Institution intended for Natural History; but still I was convinced that their subjects were so closely connected, that the habits of thought which they induced, and the mode of treating them, were so similar in many respects, that what applied to the ​one would in a great degree apply to the other. Indeed, I felt that most persons would be better prepared for the study of Natural History generally, by the study of Natural Philosophy in its various Branches, than if they were in ignorance of the latter, but there were other considerations connected with the desire I have entertained to deliver these Lectures, not so much allied to the subject of Astronomy as matters of private feeling. I have been personally long connected, not with the town of Ipswich precisely, but with the neighbourhood. I remember, with gratitude, that the first time I was shown an astronomical object of any great interest, it was exhibited to me by the founder of the mechanical and manufacturing Institution which has now risen to such great importance in the town of Ipswich. It was by the elder Mr. Ransome that I was first shown the planet Saturn, with a telescope manufactured by his own hands. And I may add, that the first Nautical Almanac I possessed, was received as a present from a gentleman then residing in Ipswich, who has now risen to great eminence in the Metropolis as an engineer. From these and other circumstances I was desirous, when the opportunity should occur, of offering to the members of the Museum, or to any other similar body in the town of Ipswich, a course of Lectures on Astronomy.

      In offering them to the authorities of the Museum, I made but one remark—that I understood it would be perfectly agreeable to the members of the Institution, and that if such were the case, it would be also exceedingly agreeable to myself, that the regulations for the attendance upon the Lectures should be framed in such a way as to give facilities of introduction to persons concerned in the mechanical operations of ​the town. And here I must beg to say, that the alliance between astronomers and mechanics is much closer than it may seem to be at the first view of the matter. Astronomers have to rely very closely upon mechanics for every part of the apparatus connected with their operations. Possibly mechanics have derived something from their connection with astronomers; but at all events, I am certain the debt is on the other side. I may adduce, as a practical instance, that the last instrument erected at the Royal Observatory, Greenwich, and to which I attach great importance, was constructed by the mechanics of Ipswich; whilst I am at the present time in negotiation with one of the mechanical establishments in the town, for another instrument of considerable importance in astronomical observations. To this I may add, that the whole of Astronomy is geometrical in its character, and that a great part of it is mechanical. I mention these things to show that the alliance between astronomers and mechanics is very close indeed; and this being the fact, I shall endeavour to do for the mechanics the best in my power. What I offer on this occasion will be offered with hearty good will, and if the Lectures be not successful, I hope the failure will have arisen from no fault of my own.

      Perhaps I may be allowed to make another remark. I should wish to invite especially the attention of those who are commonly called working-men, to the few Lectures I propose to deliver. The subjects upon which I have to treat are commonly regarded as rather beyond their reach; I take this opportunity of saying that the subjects of the Lectures will not be beyond any working-man's comprehension. Everybody who has examined the history of persons ​concerned in the various branches of science, has been enabled to learn that, whereas on the one hand those who are commonly called philosophers may be as narrow-minded as any other class, and as little informed; so on the other hand, those who have to gain their daily livelihood by handicraft, may associate their trades or businesses, whatever they may be, with accomplishments of the most perfect and the most elevated kind. I think, then, it is right I should repeat, that these Lectures will be directed in some measure with the object of being perfectly comprehended, by that class of people. It is not my object, however, to deal with what may be called the picturesque in Astronomy. I have proposed it to myself as a special object, to show what may be comprehended, by persons possessing common understandings and ordinary education, in the more elevated operations of astronomical science. The Lectures will be, therefore, of what I may call a mathematical kind. But in speaking of this, I beg that the ladies present will not be startled. I do not mean to use algebra or any other science, such as must be commonly of an unintelligible character to a mixed meeting. When I used the word mathematical, I mean that it will be my object, to show how the measure of great things may be referred to the measure of smaller things; or to sum up in few words, it will be my object in an intelligible way, to show the great leading steps of the process by which the distance of the sun and the stars is ascertained by a yard measure—the process by which the weight of the sun and the planets is measured by the pound weight avoirdupois. Occasionally I shall be prepared to go into details; but my principal business will be to show the great steps upon which those who wish to ​study Astronomy may enter, and by which they may attain a general comprehension of the rules which will lead them from one step to another.

      I shall now proceed with my subject.

      We will consider what are the general phenomena of the motion of the stars which are to be observed on any fine night. I must observe in the first place, that I shall use the term east to denote the whole of the horizon extending from the north point, through the east point, to the south point; the term west to denote the whole of the horizon extending from the south point, through the west point,

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