336 LAPLACE. 
The movements of the moon proved a fertile mine of 
research to our great geometer. His penetrating intellect 
discovered in them unknown treasures. He disentangled 
them from every thing which concealed them from vulgar 
eyes with an ability and a perseverance equally worthy 
of admiration. The reader will excuse me for citing 
another of such examples. 
The earth governs the movements of the moon. The 
earth is flattened, in other words its figure is spheroidal. 
A spheroidal body does not attract like a sphere. ‘There 
ought then to exist in the movement, I had almost said in 
the countenance of the moon, a sort of impression of the 
spheroidal figure of the earth. Such was the idea as it 
originally occurred to Laplace. 
It still remained to ascertain (and here consisted the 
chief difficulty), whether the effects attributable to the 
spheroidal figure of the earth were sufficiently sensible 
not to be confounded with the errors of observation. It 
was accordingly necessary to find the general formula of 
perturbations of this nature, in order to be able, as in the 
ease of the solar parallax, to eliminate the unknown 
quantity. 
The ardour of Laplace, combined with his power of 
analytical research, surmounted all obstacles. By means 
of an investigation which demanded the most minute at- 
tention, the great geometer discovered in the theory of 
the moon’s movements, two well-defined perturbations 
depending on the spheroidal figure of the earth. The 
first affected the resolved element of the motion of our 
satellite which is chiefly measured with the instrument 
known in observatories by the name of the transit in- 
strument ; the second, which operated in the direction 
north and south, could only be effected by observations 
