310 ; LAPLACE. 
This rank, which was lost for a moment, was bril- 
liantly regained, an achievement for which we are in- 
debted to four geometers. 
When Newton, giving to his discoveries : a generality 
which the laws of Kepler did not imply, imagined that 
the different planets were not only attracted by the sun, 
but that they also attract each other, he introduced into 
the heavens a cause of universal disturbance. Astrono- 
mers could then see at the first glance that in no part of 
the universe whether near or distant would the Kep- 
lerian laws suffice for the exact representation of the” 
phenomena; that the simple, regular movements with 
which the imaginations of the ancients were pleased to 
endue the heavenly bodies would experience numerous, 
considerable, perpetually changing perturbations. 
To discover several of these perturbations, to assign 
their nature, and in a few rare cases their numerical 
values, such was the object which Newton proposed to 
himself in writing the Principia Mathematica Philo- 
sophie Naturalis. 
with a similar arc measured in Lapland, from which it appeared that 
the length of a degree of the meridian increases from the equator 
towards the poles, conformably to what ought to result upon the sup- 
position of the earth having the figure of an oblate spheroid. The 
length of the Lapland arc was determined by means of an expedition 
which the French Government had despatched to the North of Europe 
for that purpose. A similar expedition had been despatched from 
France about the same time to Peru in South America, for the pur- 
pose of measuring an arc of the meridian under the equator, but the 
results had not been ascertained at the time to which the author 
alludes in the text. The variation of gravity at the surface of the 
earth was established by Richer’s experiments with the pendulum at 
Cayenne, in South America (1673-4), from which it appeared that the 
pendulum oscillates more slowly—and consequently the force of gray- 
ity is less intense—under the equator than in the latitude of Paris — 
Translator. 
