The log is a small triangular piece of wood, secured to the end of a long line, on which divisions are marked, bearing the same proportion to a mile which a half-minute bears to an hour. One man holds a half-minute glass in his hand--another a reel on which the line is rolled--a third, the mate, takes the log and heaves it overboard, drawing off the line with his left hand. Thus, as the log remains stationary in the water, according to the number of divisions or knots run off while the sand in the glass is running, will be shown the number of miles the ship is going in the hour. Instead of miles, the word knots is used, evidently from the knots marked on the line. The mode I have thus briefly described of finding the ship's course is called "dead reckoning." This, of course, is liable to errors, as careless steering, the compasses being out of order, or a current, may carry her far from her supposed position; at the same time, when the sky is obscured, it is the only mode of finding the way across the ocean. It can be correctly ascertained by observation of the sun, moon, and stars, taken with a sextant and a chronometer; but I shall be led to give an epitome of the science of navigation if I attempt to explain the mode of using them. In shallow waters, where the bottom has been accurately surveyed, a clever pilot will find his way with the lead. At the end of the lead a cavity is made, which is filled with grease; and according to the sort of mud, sand, or shells which adhere to it, he tells his position. This, and many other parts of navigation, Mr Bell, during our night watches, took great pains to explain to me; but it was not till I had been some time at sea that I comprehended them clearly. Mr Bell never spoke to me in the day-time; for if the captain saw him, he was certain to send me to perform some kind of drudgery or other. I was set to do all the dirty work in the ship, to black down the rigging, to grease the masts, etcetera, etcetera; indeed, my hands were always in the tar-bucket; but it served the useful purpose of teaching me a seaman's duty, and of accustoming me to work. The captain and first mate's abusive language, however, I could not stand; and my feelings resented it even more than the blows they were continually dealing me. I have said little about the emigrants. If my lot was bad, theirs was much worse. They were looked upon by the officers as so many sheep or pigs, and treated with no more consideration. Crowded together below, allowed to accumulate filth and dirt of every description, their diet bad and scanty, and never encouraged to take the air on deck, disease soon broke out and spread among them. Old and young, married and single of both sexes, were mingled indiscriminately together; and the scenes I witnessed when I was obliged to go below turned me sick with disgust, as they made my heart bleed with sorrow.