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 

 case 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 investi s:ation which demanded the most minute at- 



o 



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. Tlie 

 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 



