Mr. Rittenhouse observes, (in his Oration delivered before the American Philosophical Society, in 1775,) that “Galileo not only discovered these moons of Jupiter, but suggested their use in determining the longitude of places on the earth; which has since been so happily put in practice, that Fontenelle does not hesitate to affirm, they are of more use to geography and navigation, than our own moon.”—This great man, one of the first restorers of the true principles of physics, was condemned by, and suffered the penalties of the Inquisition, in 1535, for defending the system of Copernicus! He died in 1542. A letter from Andrew Ellicott, Esq. to Mr. Robert Patterson, dated the 2d of April 1795, and published in the fourth volume of the American Philosophical Society’s Transactions, contains sundry observations of the immersions of the satellites of Jupiter, made at Wilmington in the state of Delaware, by Messrs. Rittenhouse, J. Page, Lukens and Andrews, respectively, on divers days from the 1st to the 23d of August (both included,) in the year 1784; together with those observed at the Western Observatory, by Messrs. Ellicott, Ewing, Madison, &c. on divers days from the 17th of July to the 19th of August (both included,) in the same year: also, of the emersions of those satellites, by the same Eastern Observers, from the 29th of August to the 19th of September (both included,) and by the same Western Observers, from the 27th of August, up to the 19th of September, both included; all in the year 1784. These observations were made, “Le Trident de Neptune est le Sceptre du Mond.”[27a] when those able geometricians and astronomers were employed in ascertaining the Western Boundary of Pennsylvania, by determining the length of five degrees of longitude, West, from a given point on the river Delaware. Footnote 27a: “The trident of Neptune is the sceptre of the world.”—This, as Lalande observes, is nearly what Themistocles said at Athens, Pompey at Rome, Cromwell in England, and Richelieu and Colbert in France. ----- “It is to astronomy,” says Mr. Lalande, “that we are indebted for the first voyages of the Phœnicians, and the earliest progress of industry and commerce: it is likewise to it, that we owe the discovery of the New World. If there remain any thing to desire for the perfection and security of navigation, it is, to find the longitude at sea.” In continuation, he says:— “The utility of navigation for the welfare of a state, serves to prove that of astronomy. But it seems to me, that it is difficult for a good citizen to be ignorant, now, of the usefulness of navigation; above all, (says Lalande, feelingly,) in France. The success of the English, in the war of 1764, has but too well shewn, that a marine alone governs the fortune of empires, their power, their commerce; that peace and war are decided on the ocean; and that, in fine, as Mr. Miere has expressed it,—