RESEARCHES ON JUPITER’S SATELLITES. 341 
youthful and which communicated itself to able coad- 
jutors, 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 de- 
manded. The ship, the sport of the winds and tem- 
pests, has no occasion, in the present day, to be afraid 
of losing itself in the immensity of the ocean. An in- 
telligent 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 ex- 
isting tables of the moon entitles Laplace to be ranked 
among the benefactors of humanity.* 
In the beginning of thé year 1611, Galileo supposed 
that he found in the eclipses of Jupiter’s satellites a sim- 
ple and rigorous solution of the famous problem of the 
longitude, and active negotiations were immediately com- 
menced 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 
* The theoretical researches of Laplace formed the basis of Burck- 
hardt’s Lunar Tables, which are chiefly employed in computing the 
places of the moon for the Nautical Almanac and other Ephemerides. 
These tables were defaced by an empiric equation, suggested for the 
purpose of representing an inequality of long period which seemed to 
affect the mean longitude of the moon. No satisfactory explanation 
of the origin of thjs inequality could be discovered by any geometer, 
although it formed the subject of much toilsome investigation 
throughout the present century, until at length M. Hansen found it 
to arise from a combination of two inequalities due to the disturbing 
action of Venus. The period of one of these inequalities is 273 years, 
and that of the other is 239 years. The maximum value of the 
former is 27//-4, and that of the latter is 23//-2.— 7’ranslator. 
