oat a! v = 
Sc | 
Oe 
ral a 
328 ‘ LAPLACE. 
shine with a brighter lustre. Still, the question remained 
undecided. The inutility of such efforts seemed to sug- 
gest only a feeling of resignation on the subject, when 
from two disdained corners of the theories of analysis, 
the author of the Mécanique Céleste caused the laws of 
these great phenomena clearly to emerge. The varia- 
tions of velocity of Jupiter, Saturn, and the Moon flowed 
then from evident physical causes, and entered into the 
category of ordinary periodic perturbations depending 
upon the principle of attraction. The variations in the 
dimensions of the orbits which were so much dreaded re- 
solved themselves into simple oscillations included within 
narrow limits. Finally, by the powerful instrumentality 
of mathematical analysis, the physical universe was again 
established on a firm foundation. 
I cannot quit this subject without at least alluding to 
the circumstances in the solar system upon which depend 
the so long unexplained variations of velocity of the 
Moon, Jupiter, and Saturn. 
The motion of the earth around the sun is mainly 
effected in an ellipse, the form of which is liable to vary 
from the effects of planetary perturbation. These altera- 
tions of form are periodic ; sometimes the curve, without 
ceasing to be elliptic, approaches the form of a circle, 
while at other times it deviates more and more from that 
form. From the epoch of the earliest recorded observa- 
tions, the eccentricity of the terrestrial orbit has been 
diminishing from year to year; at some future epoch the 
orbit, on the contrary, will begin to deviate from the form 
of a circle, and the eccentricity will increase to the same 
extent as it previously diminished, and according to the 
same laws. 
Now, Laplace has shown that the mean motion of the 
