202 



SCIENCE, 



[Vol. IV., No. 83. 



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, micrometric observations are in order, 

 upon the individual stars in different clusters, to as- 

 certain 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, else- 

 where, upon stellar parallax, new hopes arise that we 

 may soon come to some wider knowledge of the sub- 

 ject; that, instead of a dozen or so parallaxes of 

 doubtful precision, we may get a hundred or more 

 relating to stars of widely different brightness and 

 motion, and so be enabled to reach some trust- 

 worthy generalizations 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 vigor- 

 ously prosecuted by Professor Pickering in this coun- 

 try, and many others elsewhere, upon the brightness 

 of the stars, and the continual variations in this 

 brightness. Since 1875, stellar photometry has be- 

 come almost a new science. 



Then, there are more than a myriad of double and 

 multiple stars to watch, and their orbits to be deter- 

 mined; and the nebulae claim keen attention, since 

 some of them appear to be changing in form and 

 brightness, and are likely to reveal to us some won- 

 derful secrets in the embryology of worlds. 



Each star also presents a subject for spectroscopic 

 study; for although, for the most part, the stars may 

 be grouped into a very few classes from the spectro- 

 scopic point of view, yet, in detail, the spectra of ob- 

 jects belonging to the same group differ considerably 

 and significantly, almost as much as human faces do. 



For such investigations, new t instruments are 

 needed, of unexampled powers and accuracy, some 

 for angular measurement, some for mere power of 

 seeing. Photography comes continually more and 

 more to the front; and the idea sometimes suggests 

 itself, 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 not 

 yet, however, most certainly. Indeed, it can never 

 come at all, as relates to certain observations; since 

 the human eye and mind together integrate, so to 

 speak, the impressions of many separate and selected 

 moments into one general view, while the camera can 

 only give a brutal copy of an unselected state of things, 

 witli all its atmospheric and other imperfections. 



New methods are also needed, I think (they are 

 unqestionably 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 instru- 

 mental errors, due to differences of temperature, to 



mechanical strains, and to inaccuracies of construc- 

 tion. Astronomers are now coming to the investiga- 

 tion of quantities so minute, that they would be 

 completely masked by errors of observation that for- 

 merly were usual and tolerable. The science has 

 reached a stage, where, as was indicated at the begin- 

 ning of this address, it has to confront and deal with 

 the possible unsteadiness of the earth's rotation, 

 and the instability of its axis. The astronomer 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 closing 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 insists, 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, perhaps, that the investigation of 

 the solar radiation, and the behavior 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 it will not. Pos- 

 sibly, too, some few other astronomical investigations 

 may facilitate the determination of latitudes and 

 longitudes, and so help exploration and commerce ; 

 but, with a few exceptions, 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, the intelligent and intellectually cul- 

 tivated will generally obtain a more comfortable live- 

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

 ignorant. Intelligence and brains are most power- 

 ful 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 ' prac- 

 tical 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 considerations, which 

 lie one side of our relations in this association, there 



