Page images

motion are from 23° 53', with the perpendicular line, to 22° 54', or through an angle of *59′. In the year 2000 B. C. it had the former greater angle, and it is predicted that somewhere about 6000 A. D. the lesser limiting angle will be reached. At the present time the angle is decreasing; though it is very close to 231⁄2°. The seventh motion, or rather variation of motion in the Earth's course are its perturbations. This term is applied to the slight alterations in the elliptic form of the Earth-path, about the Sun. It consists, at one time of a flattening of the curve of the orbit, and at another, of an increase in the degree of curvature as the Earth approaches or recedes from its planetary neighbors. These perturbations can be calculated before hand for each case.

The eighth and last motion of our Earth is through space, together with the Sun and the whole of our solar system. This motion, as far as can be judged up to the present time, is in an apparently straight line. It is in the direction of the star known as π Herculis. The rate of advance along this line is at the prodigious speed of 1,296,000 miles per day. The apparently straight line upon which the Earth, Sun and planets are traveling, has been held by some to be really a curve of great magnitude, having for its centre, 7 Tauri, more familiarly known as Alcyone-the brightest star in the Pleiades.

Briefly to recapitulate:-We have traced in merest outline five proper motions of the Earth, viz: The diurnal, the annual, the precession of the equinoxes, the advance of the apsides, and the motion through space. The modifications of motion, if they may be so called, appear to be three in number: nutation, the perturbations and the tilting of the ecliptic. This division is suggested as an easy method of classification, though the reader may prefer, with perfect propriety, to alter the classification for himself. It is, however, a wonderfully complex picture presented by our Earth, as it spins, and circles, nods and sways, rolls and rushes with terrific speed, on through space; never in reality passing through or near the same point again, once it has quitted it. It moves onward with resistless sweep, majestically, without jar or tremor of motion. With no hint of its rapid flight, it hastens on, to its appointed goal, working out its destiny in the appointed way, fulfilling as it goes, the inspired words which tell us that "while the Earth remaineth, seed time "and harvest, and cold and heat, and summer and winter, and "day and night shall not cease."


Professor Young, on the authority of J. Herschel, gives the lower limit as 2314 and the variation not to exceed 1° 20' from the mean.-ED.


Roughly, our members may be divided into three classes, viz.: -First, the professional astronomers, connected with established Observatories, and having at their disposal, more or less ample instrumental equipment. Second, amateurs having instruments fitted for serious work and possessing, moreover, a fair amount of experience in the use of such instruments. And third, members who are students of astronomy, but who are either not possessors of instruments at all, or who have not facilities for observational work of an original kind. This third class may possibly be advantageously subdivided as I shall indicate later on.

As regards the first class, the professional astronomers, it is, I am sure, a great satisfaction to us all that we have been able to enroll so many of them in our ranks. A reference to our list of members will show that it includes professional astronomers in nearly every civilized country, men whose names are household words, and the history of whose work constitutes to a great extent the history of the recent progress of our science. It is impossible to overrate the value to our association of the collaboration of these professional astronomers. Their contributions to our publications may be comparatively few, for, as a rule, the accounts of their researches are, almost of necessity, issued through other channels; but we are indebted to them for some very valuable papers, while we have constantly benefitted by their presence at our meetings and by their aid in various ways. Without them the status of our association would certainly not be what it now is.

Next, as to the second class, that consisting of amateurs possessing more or less excellent instrumental equipments. It is this class which has formed the backbone of our observing sections, and to it is due the bulk of the original work which has been recorded in the publications of the association. In the admirable address delivered from this chair last year by our valued VicePresident, Mr. Wesley, special reference was made to the organization of our observing sections, and to the excellent work which those sections have done and are still doing. It will be quite unnecessary for me to go again over the ground which Mr. Wesley covered so thoroughly, but I do wish to strongly endorse the views which he expressed as to the value of the feature which these observing sections have formed in our organization, and as

Extract from the Presidential Address, before the British Astronomical Association delivered Oct. 25, 1899, W. H. Maw, President.

to the great debt we owe to the directors by whom these sections have been controlled. Unfortunately we have to mourn the loss during the past year of one of the most valued of these directors, Miss Brown, but if anything could console us for this loss, it is the knowledge that the work which she so ably inaugurated, and which she carried on until the last with such conspicuous ability and enthusiasm, will be continued with the most conscientious thoroughness under the new director, Farther Cortie.

It is satisfactory to know that this second class of our members upon whom we depend so much for original work, is an ever growing one, while year by year it is becoming possessed of more powerful and more perfect instruments. And this brings me to a point on which I wish to say a few words, namely, the influence of the large telescopes, with which some of our more important Observatories are now provided, on the usefulness of the work of amateur observers. In considering this point it must be borne in mind that the great telescopes of the present day are of a very different class from the giant instruments of the past. The great reflectors of Herschel, of Lassell, and of Rosse were all instruments made and used by amateur astronomers, and although they possessed great light-grasp and did some admirable work they were, owing largely to the nature of their mountings, utterly unfitted for the class of observations on which the large telescopes of the present day are chiefly employed. The 36-in. and 60-in. reflectors of Dr. Common may, perhaps, be regarded as the latest of this older class of large telescopes, although it would probably be more just to consider Dr. Common's instruments as forming a connecting link between the giants of the past and present.

In the case of such large refractors as those at Pulkowa, at Washington, at Vienna, at Mount Hamilton, at Nice, at the Yerkes Observatory, and at Greenwich the cost of the telescope itself is but a small portion of the total outlay incurred. Not only must such an instrument be thoroughly well mounted to fit it for modern research work, but it must be protected by a well constructed dome, and in order that every moment of good seeing may be utilized, provision should be made for effecting all movements of both telescope, and dome with the least possible amount of labor to the observer using the instrument. How perfectly this can be done is well shown by the great Yerkes refractor, which, notwithstanding its enormous size and weight, can, with its dome, be so readily handled by the electric motors with which it is provided, that it can be-and is-efficiently used by a single

observer through a whole night, without any assistance whatever. It is satisfactory to know that two of our own members, Messrs. Warner and Swasey, were responsible for both the design and construction of this admirably perfect mounting, while the rising floor, which forms such an important feature in the equipment of both the Yerkes and Lick Observatories, and contributes so much to the convenient use of these large telescopes, is the invention of another of our members, Sir Howard Grubb.

But by the time a refractor of this kind has been erected and equipped the outlay upon it will have become so large, that it would be utter folly to use the instrument for work other than that for which its great power renders it specially fitted. The result of this is that our modern giant telescopes are, with few exceptions, employed, not in doing work which was formerly done by smaller instruments, but in doing work which formerly could not be done at all. Such for instance, is the bulk of stellar' spectroscopic work including determinations of velocity in the line of sight, the measurement of close double stars, the spectroscopic examination of nebulae, the discovery of new planetary satellites, and similar matters. We see, therefore, that the establishment of these powerful telescopes has been accompanied by the development of new fields of research, and that the work which was formerly done-ard can still be well done-by instruments of moderate size, has not been reduced. On the other hand, many professional astronomers have withdrawn from the work which they formerly did with the instruments then available, and they have thus left to amateur observers the continuance of their former labors.

We thus see that there is ample work for the members forming our observing sections and that such work, if faithfully carried out and recorded with judgment and discrimination, is calculated to be of great and permanent value.

This brings me to a somewhat delicate point on which it is, I think, my duty to say a few words:-I mean the character of the reports of our observing sections. Now the report of a section may be of two kinds, namely, it may be a simple record. of all the work done by the members of that section; or it may be a digest of the facts which the labors of the section have elicited. A report of the first kind possesses the advantage that it gives full credit for the work of individual observers, and so far acts as an encouragement to further efforts; but one is apt to rise from the perusal of such a report with a very confused idea of what it all means, and as a document for reference it

certainly leaves much to be desired. A report of the second kind, on the other hand, if carefully drawn up by an observer having special experience in the matters dealt with, such as the director of a section naturally possesses, is a work not merely of great present interest, but of permanent value, and adds materially to the standing of the society by which it is published. If our funds were abundant we might, no doubt with advantage, give our sectional reports a dual character, publishing more or less in full the records of individual observations, and adding a digest of the facts deduced by the director from those observations. In this way we should be imitating the procedure of a Royal Commission, which accompanies its report by a reprint of the evidence on which that report is founded. But, unfortunately, our funds are far from being abundant, and we are, therefore, bound to practice strict economy, and to endeavor to spend our money so that it may be of the greatest benefit to our members generally. It is thus eminently desirable that our sectional reports should be of the character of digests of facts prepared by the directors, and that the engravings should be only such as are required to illustrate these facts and render clear points which can not be so well explained verbally. I fear that the adoption of this course may lead to some disappointment of individual workers, and to the non-publication of many admirable drawings which, if our funds allowed, we should be most desirous to reproduce. I hope, however, that members of sections will see the necessity of the course I have foreshadowed, and that they will, at all events for the present, be content with a less full record of their individual work than that to which they may possibly deem they are entitled.

And this brings me to another point, namely, the mode of recording the work of our sections. While it is at present impossible for us to print anything like full records of the work of individual observers, it is eminently desirable that such records should be available for future reference. In order that this end. may be conveniently attained, however, it is essential that the reports of the observers forming any section should be sent to the director in some uniform style, and written on paper of a standard size. The selection of the form of the individual reports is, of course, to a great extent a matter to be decided by the directors of sections; but I think that all directors might agree as to a uniform size and character of paper, and I would suggest ruled foolscap would be as convenient as any. Every report of an observation, however brief, should be written on paper of the

« PreviousContinue »