Evening star. [volume] (Washington, D.C.) 1854-1972, 1902-12-30
Annual Address of President
Hall Before the Scientists.
HISTORICAL SKETCH
SCIENCE CLOSELY CONNECTED
WITH AFFAIRS OF LIFE.
Periods of Six Ancient Planets Known
to Hipparchus $50 B. C.-Equa-
lions Of Motion.

The annual address of President Asaph
Hall of the American Association for the
Advancement of Science which was deliv-
cred last night before that body. was on
the subject Of the advance made in astron-
omy. Mr.. Halls treatment of the subject,
together with the importance usually at
tached to the annual address of the presi-
dent of the association, made the occasion
stand out as perhaps the pinnacle Of the
work of the organization at the present
meeting He said:
IT take for the subject of my address the
science of astronomy, and propose to give
brief historical sketch of 1t. to consider
it's future development, and to speak OF the
influence of the sciences on civilization.
1.-The science of astronomy is so closely
connected with the affairs Of life, and is
brought into use so continuously and in
such a systematic manner, that most peo-
pie never think Of the long labor that has
been necessary to bring this science to Its
present condition. In the early times 1t
was useful to the legislator and the priest,
for keeping records, the times of public
ceremonies and of religious festivals. 1t
slowly grew into the form of :; science, and
became able to make predictions with some
certainty. This was many centuries ago.
Hipparchus, who lived $50 b. c., knew the
periods of the six ancient planets with
considerable accuracy.
Of Ancient Origin.
1.-THE results indicate that more than
two thousand years ago there existed re-
corded observations Of astronomy. Hip
parchus appears to have been one of those
clear-headed men who deduce results from
observations with good Judgment. There
tronomers had conceived the heiiocentric
motions of the planets, but this true theory
was set aside by the ingenious Ptolemy,
who assumed the earth as the center Of
motion, and explained the apparent mo-
lions of the planets by epicycles so well
that his theory became the one adopted
in the schools of Europe during fourteen
centuries. The Ptolemaic theory fattered
the egotism of men by making the earth
the center of motion, and it corresponded
well with old legends and myths. so that
it became inwoven with the literature, art
and religion of those times. Dante's con-
struction of hell, purgatory and paradise
is derived from the Ptolemaic theory of
the universe. His ponderous arrangement
Of ten divisions Of paradise with ten pur-
gatories, and ten hells, are said by some
Dante to put away his friends and his
enemies. but 1t is all derived from the pre-
vailing astronomy. Similar notions will
be found in Milton, but modified by the
lucas Oh COpeTnlcuS, WHICH Milton ndQ learn
ed in Italy. The Copernican theory won
it's way slowly, but surely, because it is
the system of nature, and all discoveries in
theory and practical astronomy helped to
show its truth; kepler's discoveries in as
tronomy, Galileo's discovery Of the laws
of motion and Newton's discovery of the
law of gravitation, put the Copernican
theory on solid foundation. Yet it was
many years before the new theories were
fully accepted. DR.. Johnson thought per-
secution a good thing, since it weeds out
false men and false theories. The Coperni-
can and Newtonian theories have stood the
test of observation and criticism, and they
now form the adopted system of as
tronomy.
The Equations of Motion.
1.-The laws of motion, together with the
law of gravitation, enable the astronomer
to form the equations of motion for the
bodies of our solar system; 1t remains to
solve these equations, to correct the orbits,
and to form tables of the sun, moon and
the planets. This work was begun more
than century ago, and it has been re-
peated for the principal planets several
times, so that now we have good tables of
these bodies. In the case of the principal
planets the labor of determining their
orbits was facilitated by the approximate
orbits handed down to by the ancient
astronomers, and also by the peculiar con-
ditiOnS of these orbits. For the most part
the orbits are nearly circular; the planets
move nearly in the same plane and their
motions are in the same direction. The gen.
eral problem of determining orbit from
three observations, which furnish the nee
essary and sufficient data, was not solved
until about century ago. The orbits Of
comets were first calculated with some pre-
clston. Attention was called to these bodies
by their threatening aspects, and by the
terror they inspired among people. 1t was
therefore happy duty of the astronomers
to show that the comets also move in orbits
around the sun, and are subject to the
same laws as the planets. This work was
easier because the comets move nearly in
parabolas, which are the simplest of the
comic sections.
Conditions Of Solar System.
Good preliminary orbits can now be COM
puted for comets and planets without much
labor. This, however, is only beginning
Of the work of determining their actual
motions. The planets act on each other and
on the comets, and it is necessary to COM
pute the result of these forces. Here, again.
the conditions of our solar system furnish
peculiar advantages The great mass Of
the eXerts such a superior force that
the attractions OF the planets are relatively
small, so that the first orbits, computed by
neglecting this interaction, are nearly cor
rect. But the interactions Of planets be-
come important with the lapse of time,
and the labor Of computing these perturba-
tions is very great This work has been
done repeatedly and We now have good
| numerical values of the theories of the
principal planets, from which tables can
be made. Practically, therefore, this ques-
ton appears to be well toward final solu-
| ton. But the whole story has not been
| told.
THE planets on account of their relative
| distances being great and because their
| figures are nearly spherical can be consid-
! cred material particles and then the
| equations of motion readily formed.
THE elements of the orbits are supposed
| to be continually changed by the attractions
| Of the other planets. By means Of this
| theory, and the mathematical machinery
| given by Lagrange, which can be applied
| to a great variety of questions, the observa-
| tions Of the planets can be satisfied over
| long intervals of time. When this theory
! Of the motions was carried out a century
| ago it appeared that the great problem of
| planetary motion was near a complete So
| luton. But this solution depends on the
use of SERIES which undergo integrations
| that may introduce small divisors An ex-
animation Of these series by Hansen, Pom
! care and others indicates that some of
| them not convergent. Hence the con-
| illusions formerly drawn about the stability