LAPLACE. 153 



Laplace had not proved that the law need only have been approximate 

 at the origin, and that the mutual action of the satellites has sufficed 

 to render it rigorous. 



The illustrious geometer who always pursued his researches to their 

 most remote ramifications arrived at the following result: The action 

 of Jupiter regulates the movements of rotation of the satellites, so 

 that, without taking into account the secular perturbations, the time of 

 rotation of the first satellite, plus twice the time of rotation of the third, 

 forms a sum which is constantly equal to three times the time of rota- 

 tion of the second. Influenced by a deference, a modesty, a timidity, 

 without any plausible motive, our artists in the last century surren- 

 dered to the English the exclusive privilege of constructing instruments 

 of astronomy. Thus, let us frankly acknowledge the fact, at the time 

 when Herschel was prosecuting his beautiful observations on the other 

 side of the Channel, there existed in France no instruments adapted 

 for developing them ; we had not even the means of verifying them. 

 Fortunately for the scientific honor of our country, mathematical analy- 

 sis is also a powerful instrument. Laplace gave ample proof of this 

 on a memorable occasion when, from the retirement of his chamber, he 

 predicted, he minutely announced, what the excellent astronomer of 

 Windsor would see with the largest telescopes which were ever con- 

 structed by the hand of man. 



When Galileo, in the beginning of the year IGIO, directed toward 

 Saturn a telescope of very low i)ower, which he had just executed with 

 his own hands, he perceived that the planet was not an ordinary globe, 

 without, however, being able to ascertain its real form. The expression 

 " tri-corporate,'" by which the illustrious Florentine designated the appear- 

 ance of the planet, implied even a totally erroneous idea of its struc- 

 ture. Our countryman Roberval entertained much sounder views on 

 the subject, but from not having instituted a detailed comparison be- 

 tween his hypothesis and the results of observation, he abandoned to 

 Huyghens the honor of being regarded as the author of the true theory 

 of the phenomena presented by the wonderful planet. Every person 

 knows in the present day that Saturn consists of a globe about 000 

 times greater than the earth, and a ring. Tliis ring does not touch 

 the ball of the planet, being everywhere removed from it at a distance 

 of 20,000 (English) miles. Observation indicates tiie breadth of the 

 ring to be 54,000 miles. The thickness certainly does not exceed 250 

 miles. With the exception of a black streak, which divides the ring- 

 throughout its whole contour into two parts of unequal breadth and 

 of different brightness, this strange, colossal bridge without piles had 

 never ottered to the most experienced or skillful observer either spot 

 or protuberance adapted for deciding whether it was immovable or 

 endued with a movement of rotation. 



Laplace considered it to be very improbable, if the ring was immov- 

 able, that its constituent parts should be capable of resisting by their 



