The great difficulty of making observations at sea, except with a sextant--and such, it must be remembered, are of a very rough nature compared with those made on shore--is want of steadiness. The sea is never quiet, and no machine has as yet been invented to counteract the movement of a ship, and obtain a perfect level. Mr Vernon, the clergyman passenger I spoke of, told me an anecdote of Galileo, showing that, great as he was as an astronomer, he might make a great mistake by forgetting to take all points into consideration. He fancied that he had discovered a method of determining longitudes at sea by observing the eclipses of Jupiter's satellites. He accordingly went to the King of Spain and offered to manufacture telescopes to enable his navigators to sail across the ocean without fear or hesitation. His telescopes were unexceptionable, and his method excellent, but it depended entirely on the perfect steadiness of the observer; and, as even the biggest ships of the mighty monarch of Spain could not be taught to keep quiet, the great astronomer's telescopes were perfectly useless. I was much struck with the fine deep Prussian blue of the waters, which had changed from the cobalt bine of more northern latitudes, as also with its extraordinary power to froth and effervesce. The water, as it was dashed about the decks in the morning from the buckets, sparkled like champagne; but perhaps that was owing more to the nature of the atmosphere than to any peculiarity in the water.