SCIENCE. 



127 



with small instruments what at common altitudes can be 

 done only with large ones ; and when possible it is always 

 better to use small instruments, since they are more easily 

 handled, and are relatively stronger and better than largs 

 ones. Uniformity of temperature may be secured by seek- 

 ing locations in the tropical islands, or on the coasts like 

 that of California, where the ocean winds keep the temper- 

 ature nearly uniform throughout the year. At great 

 altitudes we may secure a clearness of vision that would be 

 of the greatest value in the examination of faint objects, 

 and by this means, and by persevering and continuous ob- 

 servation, interesting discoveries may be made. It is a 

 matter of course that, except in the case of comets, the future 

 discoveries in astronomy will belong to faint and delicate 

 objects ; but these are interesting, and should not be 

 neglected. A uniform temperature, which secures good 

 definition, and steady images of the stars, is necessary for 

 accurate determinations of position, and for all measure- 

 ments of precision. This condition is especially important 

 in such work as that of stellar parallax, the determination 

 of the constant of aberration, and wherever the yearly 

 change of temperature may act injuriously. In the selection 

 of better sites for observatories, I think we have an easy 

 means of advancing astronomy. 



As this science grows and expands, it will become more 

 and more necessary to study the economy of its work, in 

 order that astronomers may bestow their labors in the most 

 advantageous methods, and may rid themselves of all cum- 

 bersome and time-consuming processes. The manner of 

 publishing observations has already been much abbreviated, 

 and improved, I think, by some of the European astrono- 

 mers, and this change seems destined to become universal. 

 As the positions of many objects are now well known, the 

 need of printing all the details of the observation, such as 

 the transit of the wires, the readings of the micrometers, 

 etc., is very slight ; and this printing may be safely aban- 

 doned. Even this change will lead to a great saving in the 

 time and cost of printing. But this will necessitate a more 

 complete discussion of the work and a more careful examina- 

 tion of the instruments ; things to be desired, since they 

 tend to lift the observer out of his routine, and make him a 

 master of his business. There are objections to this 

 change, and some of them are real, such as the importance 

 of publishing a complete record ; but this is overestimated, 

 I think, since the original records ought always to be re- 

 ferred to in case of doubt ; and other objections are facti- 

 tious, such as the need of publishing a large a showy book 

 in order to impose on the public. 



We may hope also for improvements in theoretical astron- 

 omy, and for the better training and preparation of students 

 of this science. I know that it is sometimes said that theo- 

 retical astronomy is finished, and that nothing more can be 

 done. Such assertions come from professors who are old 

 and weary, or from those young men who tire out early in 

 life ; but they are wrong. The improvements that Hansen 

 has made in the theory of perturbations, and Poinsot's study 

 of the theory of rotation, show what careful investigation 

 may do, and assure us of further progress. It must be con- 

 fessed that some of the astronomical work done in our 

 country bears evidence that the astronomers did not under- 

 stand the correct methods of reduction, and much of it 

 shows evidence of hasty and ill-considered plans. This is 

 perhaps a natural condition for beginners, but we trust that 

 it has been outgrown. An actual need for the astronomical 

 students of our country is a good book on theoretical astron- 

 omy, similar to Pontecoulant's work, in which the whole 

 subject shall be presented in a complete form, such as we 

 find in the Me"canique Celeste, together with an account of 

 the improvements made by Gauss, Poisson, Hansen and 

 others. There is no American book of this kind, and the 

 English works are too partial, designed apparently to fit the 

 student for college examinations, and not to give him a com- 

 plete knowledge of the science. Such a book has hardly 

 been attempted in our language, unless that of Woodhouse 

 may be an exception, and it may be a long time in coming, 

 since it requires a man qualified to do the work, and will 

 involve an expense of labor in the preparation, and of cost 

 in publishing, such as few are willing to incur. In the 

 meantime it is far better for the student to go directly to the 

 writings of Lagrange and Laplace, of Gauss and Poisson 

 and other masters, rather than to spend time in reading sec- 



ond-rate authors who endeavor to explain them. And gen- 

 erally this will be found the easier way also, since the stud- 

 ent avoids the confused notions and symbols, and the 

 grotesque expressions and egotism of small men, and is 

 lifted into the region of ideas and invention. 



In presenting his exposition of the nebular hypothesis, 

 which has since become so celebrated, Laplace says : "I 

 present this hypothesis with the distrust which everything 

 ought to inspire that is not a result of observation or of cal- 

 culation." It is a singular fact that, among all the writings 

 on the nebular hypothesis, I have never seen a reference to 

 this presentation of it by its most distinguished advocate ; 

 and yet this is the true spirit of scientific astronomy. Laplace 

 did not wish to exempt his own theories from criticism, and 

 neither should anyone. In astronomy there is no final human 

 authority, no synod or council, but simply an appeal to rea- 

 son and observation. If a theory or a discovery be true, it 

 will stand the test of observation and of calculation ; if false, 

 it must pass away to that Miltonian limbo where so many 

 things have gone and are going. The question is some- 

 times asked, of what use is astronomy ? and the reply gen- 

 erally made is that it has conferred great benefits on naviga- 

 tion and on commerce, since it is by means of his astrono- 

 mical knowledge that the sailor determines the position of 

 his ship on the ocean. There is a truth in this reply, but it 

 is only partial. The great value of astronomy is that it is 

 really a science, and that it has broken the path and led the 

 way through which all branches of science must past if they 

 ever become scientific. It is the spirit of honest, unrelent- 

 ing criticism, and of impartial examination, that finally 

 eliminates error and awards to every one his just due, that 

 makes astronomy honorable and attractive ; and it is by 

 cultivating this spirit that astronomy confers its chief bene- 

 fit, for it is this that shall break in pieces and destroy all 

 false assumptions in science and in philosophy. 



JOSEPH HENRY. 



Eulogy By Professor A. M. Mayer. 

 At the meeting of the Association in 1878, a committee, com- 

 posed of Professors Baird, Newcomb and myself, was appointed 

 to prepare a eulogy on our revered and lamented colleague and 

 former president, Joseph Henry. This — I will not say labor, but 

 duty of affection — has devolved on me alone. I would that the 

 other members of this committee had laid before you their tributes 

 to his memory, because for years they had been closely associated 

 with him in his social and professional life in Washington. Yet, 

 while Professor Henry had been the friend of their manhood, he 

 was the friend of my boyhood ; and during 25 years he ever regarded 

 me — as was his wont to say — with a "paternal interest." To his 

 disinterested kindness and wise counsels is due much, very much, 

 of whatever usefulness there is in me. Hence I have said that it is 

 a duty of affection for me to speak to you about one who was my 

 beloved friend. I shall not, however, attempt a biography of 

 Joseph Henry, nor will I speak of his administrative life as director 

 of the Smithsonian Institution, for this is known and valued by the 

 whole world. His best eulogy is an account of his discoveries ; 

 for a man of science, as such, lives in what he has done, and not in 

 what he has said; nor will he be remembered in what he proposed 

 to do. I will, therefore, with your permission, confine myself 

 chiefly to Henry as the discoverer ; and I do this the more willingly 

 because I am familiar with his researches, and also because Pro- 

 fessor Henry, from time to time, took pleasure in giving me 

 accounts of these mental conceptions which preceded his work, led 

 him to it and guided him in it. Rightly to appreciate a discoverer, we 

 should not look at his work from our time, but go back and regard 

 it from his time ; we should not judge his work in the fulness ol the 

 light of present knowledge, but in the dim twilight which alone 

 illuminated him to then unknown — but now well-known — facts and 

 laws. I will, therefore, endeavor first to present you with a clear, 

 but necessarily very concise, view of the state of our knowledge of 

 electricity when Henry began his original researches in that branch 

 of science, and then point out the value of his discoveries, by show- 

 ing that they added to knowledge, and how they instigated and influ- 

 enced the discoveries and inventions of other men. Henry began his 

 electrical reseaiches at the age ot twenty-eight, in the year 1827, while 

 he was professor of mathematics and natural philosophy in the Al- 

 bany Academy. At these he continuously worked till 1832, when, a t 



