The times. [volume] (Washington [D.C.]) 1897-1901, 1901-01-13

would be seen. will forever be regard
ed as fine triumph of the human INTEL
lect.
But the results OF the enquiries which
| now concern us are generally of not so
sensational character. although they lie
at the root of our knowledge of celestial
| motions. They more often take the shape
| of tables and discussions relating to the
movements of the bodies which make up
our solar system.
| Gauss may be said to have led the way
during the present century by his 'Theo-
| ria Molus Corporum Coelestium Solem
Ambientlum.' This was a worthy sequel
to the ''Mechanique Celeste" in which
work. toward the end of the preceding
century. Laplace had enshrined all that
was known on the planetary results of
gravitation.
In later years lie verrier and Newcomb
have been among the chief workers on
whom the mantle OF such distinguished
predecessors has fallen. From them the
planet and satellite tables now in use
| have been derived.
But the motion of our own satellite, the
moon. has had Vaccinations for other ana
lysts besides those We have named.
The problem. indeed, Of the moons mo-
ton is one of the most difficult, and has
taxed the ingenuity of astronomers from
an early date. Even at the present day
1t is impossible 20 predict the exact posi-
| ton of the moon al any one moment ow-
ing to inequalities and perturbations the
exact varying qualities of which are not
| known
The two most important theories of the
motion of the moon completed toward the
| middle Of the century were due to Han
sen and DeIaunay. The formers ap-
peared In 1888. the lunar tables being pub
lished later QS50, while the latter's was
published in 1850
Hansen's theory had for its chief object
the formation of tables; to avoid the in
| convenience of using in his calculations
series which slowly converge he inserted
numerical values throughout In Hansen's
solution the problem is one actually pre-
sented by nature. allowance being made
| for every known cause Of disturbance.
There Is one disadvantage. namely. that
| should observations demand a change in
any of the constants used there is no
means of making any correction in the
| results.
( DeiduNdy $ theory SurnOunteu InlS uliif-
| Guilty. but at the expense of still greater
inconvenience for making ephemeris.
/ The slow conveyance of certain series in
volved an immense amount of labor TO
give sufficiently approximate results.
More recently, as the century is closing.
| DIR. Brown has taken up the subject and
| made a fresh attempt to calculate the mo-
ton of our satellite. 1t may be stated
! that he adopts all Delaunay's modfica-
tons of the problem and works them out
alphabetically but there are many tech
! nicaI differences which would be out OF
place to mention here.
| Enough has been stated to show that
there is not likely to be any breach OF
continuity in the treatment of this most
| important problem.
| Another attack on the moon, and incl
| dentaIly, its motion has recently been
| made by another analyst. Prof. George
| Darwin; graphing with all the conse
/ quenees of tidal friction, he has been able
| to present to us the past and future his
| tory of our satellite. Beginning as a part
of the material congeries from which SUBJ
sequently some 56,0oo.coo years ago both
earth and moon, as separate bodies. were
AS4"ie"' u mas eNei 0hAiNS NeSii
its orbit ana 50 re'featihs Iarther away
! from ITS centre OF Motion. WINE tne Pc
Rod OF the eartns rotation mas been IN
creasins at the same time from possible
period of some three hours when the
/ moon was born to one OF l-ieo hours Wnen
| the day and month VIII De equal, some
thing Ike lSoVS''os" years peihs required
for the process.
| STELLAR EVOLUTION
1t was Only in the Sos, after thousands
| of observations of the spectra of stars,
nebuIae, and comets had been secured.
that the full meaning of the revelations Of
the spectroscope began to dawn upon the
world
Before the introduction of spectrum an
alysis all stars were supposed to be suns,
and the only difference recognized among
| them was one of brilIiancy and the va
| Ration of brilliancy in the cage of some OF
them.
| 1t ultimately came out that great classes
might be recognized by the differences of
| their spectra. which we're ultimately
| traced to differences in their chemistry
| and in their ture. as determined
| by the extension of the spectra in the
ultra violet. the whittier stars being hotter
/ than the red ones as a white-hot poker Is
hotter than a red-hot poker
| Next there was evidence to show that
4 large proportion Of the stars were not
stars at all Ike the sun. but swans OF