Sept. 18, 1884] 



NA TURE 



507 



Prof. Newton, and others, who consider them to be strangers 

 coming in from outer space, sometimes "captured" by planets, 

 and forced into elliptic orbits, so as to become periodic in their 

 motion. Certainly this theory has strong supports and great 

 authority, and probably it meets the conditions better than any 

 other yet proposed. But the objections are really great, if nut 

 insuperable, — the fact that we have so few, if any, comets moving 

 in hyperbolic orbits, as comets met by the sun w raid be expected 

 to move : that there seems to be so little relation between the 

 direction of the major axis of cometary orbits and the direction 

 of the solar motion in space ; and especially the fact, pointed out 

 and insisted upon by Mr. Proctor in a recent article, that the 

 alteration of a comet's natural parabolic orbit to the observed 

 elliptic one, by planetary action, implies a reduction of the 

 comet's velocity greater than can be reasonably explained. If, 

 for instance, Brorsen's comet (which has a mean distance from the 

 sun a little more than three times that of the earth) was really 

 once a parabolic comet, and was diverted into its present path 

 by the attraction of Jupiter, as generally admitted, it must have 

 had its velocity reduced from about eleven miles a secon 1 to live 

 Now, it is very difficult, if not out of the question, to imagine 

 any possible configuration of the two bodies and their orbits 

 which could result in so great a change. While I am by no 

 means prepared to indorse as conclusive all the reasoning in the 

 article referred to, and should be very far from ready to accept 

 the author's alterna'ive theory (that the periodic comets have 

 been ejected from the planets, and so are not their captives, but 

 their children), I still feel that the difficulty urged against the 

 received theory is very real, and not to be evaded, though it may 

 possibly be overcome by future research. 



Still more problematical is the constitution of these strange 

 objects of such enormous volume and inconceivable tenuity, self- 

 luminous and transparent, yet reflecting light, the seat of forces 

 and phenomena unparalleled in all our other experience. Hardly 

 a topic relating to their appearance and behaviour can be named 

 which does not contain an unsolved problem. The varying 

 intensity, polarisation, and spectroscopic character of their light ; 

 the configurations of the nucleus and its surrounding nebulosity ; 

 and especially the phenomena of jets, envelopes, and tail, — all 

 demand careful observation and thorough discussion. 



I think it may be regarded as certain that the explanation of 

 these phenomena when finally reached, if that time ever comes, 

 wiU carry with it, and be based upon, an enormous increase in 

 our knowledge as to the condition, contents, and temperature of 

 inter-planetary space, and the behaviour of matter when reduced 

 t 1 lowest terms of density and temperature. 



Time forbids any adequate discussion of the numerous pro- 

 blems of stellar astronomy. One work, in its very nature inces- 

 sant and interminable, consists, of course, in the continual 

 observation and cataloguing of the places of the stars, with 

 ever-increasing precision. These star-places form the scaffold 

 and framework of all other astronomical investigations involving 

 the motions of the heavenly bodies : they are the reference-points 

 and bench-marks of the universe. Ultimately, too, the com- 

 parison of catalogues of different dates will reveal the paths and 

 motions of all the members of the starry host, and bring out the 

 great orbit of the sun and his attendant planets. 



Meanwhile, micrometic observations are in order, upon the 

 individual stars in different clusters, to ascertain the motions 

 which occur in such a case ; and the mathematician is called upon 

 again to solve the problem of such movement. 



Now, too, since the recent work of Gill and Elkin in South 

 Africa, and of Struve, Hall, and others, elsewhere, upon stellar 

 parallax, new hopes arise that we may soon come to some wider 

 knowledge of the subject ; that, instead of a dozen or so 

 parallaxes of doubtful precision, we may get a hundred or more 

 relating t > stars of widely different brightness and motion, and 

 so be enabled to reach some trustworthy generalisations as to the 

 constitution and dimensions of the stellar universe, and the 

 actual rates of stellar and solar motion in space. 



Most interesting, also, are the studies now so vigorously 

 prosecuted by Prof. Pickering; in this country, and many 

 others elsewhere, upon the brightness of the stars, and the con- 

 tinual variations in this brightness Since 1875, stellar photometry 

 has become almost a new science. 



Then there are more than a myriad of double and multiple stars 

 to watch, and their orbits to be determined ; and the nebula; 

 claim keen attention, since some of them appear to be changing 

 in form and brightness, and are likely t < reveal to us some 

 wonderful secrets in the embryology of worlds. 



Each star also presents a subject for spectroscopic study ; for 



although, for the most part, the stats maybe grouped into a very 

 few classes from the spectroscopic point of view, yet, in detail, 

 the spectra of objects belonging to the same group differ 

 considerably and significantly, almost as much as human 

 faces do. 



For such investigations, new instruments are needed, of 

 unexampled powers and accuracy, some for angular measure- 

 ment, some for mere power of seeing. Photography comes 

 continually more and more to the front ; and the idea sometimes 

 suggests it elf that by and by the human eye will hardly be 

 trusted any longer for observations of precision, but will be 

 superseded by an honest, unprejudiced, and unimaginative plate 

 and camera. The time is n t yet, however, most certainly. 

 Indeed, it can never come at all, as relates to certain observa- 

 ti ns ; since the human eye and mind together integrate, so to 

 speik, the impressions of many separate and selected moments 

 into one general view, while the camera can only give a brutal 

 copy of an un elected state of things, with all its atmospheric and 

 other imperfections. 



New methods are also needed, I think (they are unquestion- 

 ably possible), for freeing time-observations from the errors of 

 personal equation ; and increased precision is demanded, and is 

 being progressively attained, in the prevention or elimination 

 of instrumental errors, due to differences of temperature, to 

 mechanical strains, and to inaccuracies of construction. 

 Astronomers are now coming to the investigation of quantities 

 so minute that they would be completely masked by errors of 

 observation that formerly were usual and tolerable. The 

 science has reached a sta^e, where, as was indicated at the 

 beginning of this address, it has to confront aril deal with the 

 possible unsteadiness of the earth's rotation, and the instability of 

 its axis. The astron imer has now to reverse the old maxim of 

 the courts: for him. and most emphatically at present, De 

 minimis curat lex. Residuals and minute discrepancies are the 

 seeds of future knowledge, and the very foundations of new- 

 laws. 



And now, in cl >sing this hurried and inadequate, but I fear 

 rather tedious, review of the chief problems that are at present 

 occupying the astronomer, what answer can we give to him 

 who ins sts, Cui bono ? and requires a reason for the enthusiasm 

 that makes the votaries of our science so ardent and tireless in 

 its pursuit? Evidently very few of the questions which have 

 been presented have much to do directly with the material 

 welfare of the human race. It may possibly turn out, per- 

 haps, that the investigation of the solar radiation, and the 

 behaviour of sun-spots, may lead to some better understanding 

 of terrestrial meteorology, and so aid agricultural operations and 

 navigation. I do not say it will be so, — in fact, I hardly expect 

 it, — but I am not sure if will not. Possibly, too, some few other 

 astronomical investigations may facilitate the determination 

 of latitudes and longitudes, and so help exploration and 

 commerce ; but, with a few exception, it must be admitted that 

 modern astronomical investigations have not the slightest 

 immediate commercial value. 



Now, I am not one of those who despise a scientific truth or 

 principle because it admits of an available application to the 

 affairs of what is called ' ' practical life, " and so is worth 

 something to the community in dollars and cents : its commercial 

 value is — just what it is — to be accepted gratefully. 



Indirectly, however, almost all scientific truth has real 

 commercial value, because " knowledge is power," and because 

 (I quote it not irreverently) " the truth shall make you free," — 

 any truth, and to some extent ; that is to say, tire intelligent and 

 intellectually cultivated will generally obtain a more comfortable 

 livelihood, and do it more easily, than the stupid and the 

 ignorant. Intelligence and brains are most powerful allies of 

 strength and hands in the struggle for existence ; and so, on 

 purely economical grounds, all kinds of science are worthy of 

 cultivation. 



But I should be ashamed to rest on this lower ground : the 

 highest value of scientific truth is not economic, but different 

 and more noble ; and, to a certain and great degree, its truest 

 worth is more as an object of pursuit than of possession. The 

 "practical life" — the eating and the drinking, the clothing and 

 the sheltering — comes first, of course, and is the necessary 

 foundation of anything higher ; but it is not the whole or the 

 best or the most of life. Apart from all spiritual and religious con- 

 siderations, which lie on one side of our relations in this Associa 

 tion, there can be no need, before this audience, to plead the 

 higher rank of the intellectual, esthetic, and moral life above 

 the material, or to argue that the pabulum of the mind is worth 



