ARTICLE IV. 
RESULTS OF RECENT RESEARCHES ON THE EVOLUTION OF THE STELLAR 
SYSTEMS. 
(Plates LV and VY.) 
BY T. J. J. SEE, A.M., Pa.D. (BrRuin), 
ASTRONOMER AT THE LOWELL OBSERVATORY. 
Read before the American Philosophical Society, January 7, 1898. 
It is now two hundred and eleven years since Newton published the Principia, 
embodying his grand generalization of the law of gravitation, and the proof of this law 
for the most obvious and fundamental phenomena of the solar system. Geometers have 
since been occupied with the development and extension of the principle discovered by 
the illustrious Newton, and have finally explained with almost entire satisfaction the 
motions and attractions of the planets, satellites, comets, and other bodies which revolve 
about the sun. This great-development can hardly fail to excite the admiration of those 
who contemplate the history of scientific progress, and must be accounted one of the most 
noble and enduring monuments of the human mind. So sublime an achievement has 
required the combined labors of a long series of men of transcendent mathematical and 
mechanical genius, each building upon the foundation laid by his predecessors. Though 
many distinguished geometers have borne an honorable part in this remarkable develop- 
ment of Physical Astronomy, it will not be inappropriate to point out the great credit for 
the perfection of the Newtonian theory due to Clairaut and Euler, Lagrange and La- 
place, Gauss and Hansen, Adams and Leverrier. Among living investigators in mathe- 
matical astronomy the names of Hill and Newcomb, Darwin and Poincaré occupy the 
foremost place. These great men have brought the mechanics of the heavens to so high 
a state of perfection that in almost every case we may now predict the heavenly motions 
as accurately as we can observe them. In view of the rapid perfection of telescopes and 
other instruments of precision, this achievement, from the intricacy of the analysis 
required in the problem, and the abstruseness of the methods used in the reduction of 
