Historical Eulogy on the Marquis De Laplace. 5 
He had at first examined whether we could explain the accelera- 
tion of the moon’s motion on supposing that the action of gravity is 
not instantaneous but subject to a successive transmission, like that 
of light. In this way, he could not discover the true cause. At last, 
a new research served his genius better. On the 19th of March, 
1787, he gave to the Academy of Sciences a solution clear, and un- 
attended. with this insurmountable difficulty. He proved very dis- 
tinetly that the acceleration observed is a necessary effect of univer- 
sal gravitation. 
This great discovery enlightened then the most important points 
of the system of the world. In effect, the same theory made him 
know that, if the action of gravitation upon the stars is not instanta- 
neous, we must suppose it propagated more than fifty million times 
faster than light, the well known velocity of which is seventy thou- 
sand leagues a second. 
He concluded still, from his theory of the Junar motions, that the 
medium in which the stars move, opposes only to the course of the 
planets a resistance, as it were, insensible; for this cause would 
above all things act upon the motion of the moon, and it peiiites 
upon it no observable effect. 
The discussion of the motions of this star is pregnant with re~ 
markable consequences. We can conclude from it, for example, . 
that the motion of rotation of the earth around its axis is invariable. 
The length of the day has not’ changed one hundredth part of a 
second, for two thousand years. It is worthy of notice, too, that an 
astronomer would have no need of leaving his observatory in order 
to measure the distance from the earth to the sun. It would suffice 
him to observe, constantly, the variations of the lunar motion: from 
these he could conclude this distance with exactness, 
A consequence still more striking is that which relates to the Saint 
of the earth; for the form itself of the terrestrial globe is imprinted 
upon certain inneeslaiee of the course of the moon. These inequal- 
ities could not exist if the earth were perfectly spherical.. We can 
determine the amount of the earth’s applatisement, (oblateness,) by 
observing the lunar motions only. The results which we have de- 
duced from them, agree with the actual measures that have been ob- 
- tained by the great geodesical voyages to the equator, to the — 
ern Regions, to India, and to divers other countries. 
a. sora at we ome his soning pars 
of modern theories 
