tables. The
immediate object of this improvement was, in effect, the promotion of
maritime intercourse between distant countries, and, what was indeed far
superior to all considerations of mercantile interest, the preservation
of the lives of mariners.

Thanks to a sagacity without parallel, to a perseverance which knew no
limits, to an ardour always youthful and which communicated itself to
able coadjutors, Laplace solved the celebrated problem of the longitude
more completely than could have been hoped for in a scientific point of
view, with greater precision than the art of navigation in its utmost
refinement demanded. The ship, the sport of the winds and tempests, has
no occasion, in the present day, to be afraid of losing itself in the
immensity of the ocean. An intelligent glance at the starry vault
indicates to the pilot, in every place and at every time, his distance
from the meridian of Paris. The extreme perfection of the existing
tables of the moon entitles Laplace to be ranked among the benefactors
of humanity.[37]

In the beginning of the year 1611, Galileo supposed that he found in the
eclipses of Jupiter's satellites a simple and rigorous solution of the
famous problem of the longitude, and active negotiations were
immediately commenced with the view of introducing the new method on
board the numerous vessels of Spain and Holland. These negotiations
failed. From the discussion it plainly appeared that the accurate
observation of the eclipses of the satellites would require powerful
telescopes; but such telescopes could not be employed on board a ship
tossed about by the waves.

The method of Galileo seemed, at any rate, to retain all its advantages
when applied on land, and to promise immense improvements to geography.
These expectations were found to be premature. The movements of the
satellites of Jupiter are not by any means so simple as the immortal
inventor of the method of longitudes supposed them to be. It was
necessary that three generations of astronomers and mathematicians
should labour with perseverance in unfolding their most considerable
perturbations. It was necessary, in fine, that the tables of those
bodies should acquire all desirable and necessary precision, that
Laplace should introduce into the midst of them the torch of
mathematical analysis.

In the present day, the nautical ephemerides contain, several years in
advance, the indication of the times of the eclipses and reappearan