present
day the nautical ephemerides contain, several years in advance, the
indications of the times of the eclipses and reappearances of Jupiter's
satellites. Calculation is as precise as direct observation.

Influenced by an exaggerated deference, modesty, timidity, France in the
eighteenth century surrendered to England the exclusive privilege of
constructing her astronomical instruments. Thus, when Herschel was
prosecuting his beautiful observations on the other side of the Channel,
we had not even the means of verifying them. Fortunately for the
scientific honor of our country, mathematical analysis also is a
powerful instrument. The great Laplace, from the retirement of his
study, foresaw, and accurately predicted in advance, what the excellent
astronomer of Windsor would soon behold with the largest telescopes
existing. When, in 1610, Galileo directed toward Saturn a lens of very
low power which he had just constructed with his own hands, although he
perceived that the planet was not a globe, he could not ascertain its
real form. The expression "tri-corporate," by which the illustrious
Florentine designated the appearance of the planet, even implied a
totally erroneous idea of its structure. At the present day every one
knows that Saturn consists of a globe about nine hundred times greater
than the earth, and of a ring. This ring does not touch the ball of the
planet, being everywhere removed from it to a distance of twenty
thousand (English) miles. Observation indicates the breadth of the ring
to be fifty-four thousand miles. The thickness certainly does not
exceed two hundred and fifty 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 foundations had never offered to the most experienced or
skillful observers either spot or protuberance adapted for deciding
whether it was immovable or endowed with a motion of rotation. Laplace
considered it to be very improbable, if the ring was stationary, that
its constituent parts should be capable of resisting by mere cohesion
the continual attraction of the planet. A movement of rotation occurred
to his mind as constituting the principle of stability, and he deduced
the necessary velocity from this consideration. The velocity thus found
was exactly equal to that which Herschel subsequently derived from a
series of extremely deli