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 large 
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 Mdcatiique 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 wcrk 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 researches at the age of 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 1833, when, at 
