Among the numerous and important advantages, then, resulting from astronomy, noticed by the celebrated Lalande (in the preface to his book, entitled _Astronomie_,) he remarks that it is well known, that besides the tendency of this science to dissipate many vulgar errors and prejudices,[26] cosmography and geography cannot go on, but by its means: that the discovery of the satellites of Jupiter has given greater perfection to our geographical and marine charts, than they could have attained by ten thousand years of navigation and voyages;[27] and, that when their theory shall become still better known, the method of determining the longitude at sea will be more exact and more easy. ----- Footnote 26: “A man would deceive himself,” says Lalande, “in believing he could be a philosopher, without the study of the natural sciences. To be wise, not by weakness, but by principles, it is necessary that, to be able to reflect and think with vigour, we be freed from those prejudices which deceive the judgment, and which oppose themselves to the development of reason and of genius. Pythagoras would not have any disciples, who had not studied Mathematics: over his door was to be read, that “no one was to enter, unless he were a geometrician.”—Morals would be less sure, and less attractive for us, if they were to be founded on ignorance or on error. “Ought we,” he asks, “to consider as of no importance the advantage of being freed from the misfortunes of ignorance? Is it possible to observe, without a feeling of compassion and even of shame, the stupidity of those, who formerly believed, that by making a great vociferation, during an eclipse of the Moon, they furnished relief to the sufferings of that (imagined) goddess; or, that these eclipses were produced by enchantment?” “Cum frustra resonant æra auxiliaria Lunæ.” Met. iv. 333.