In order to let the passengers know the result, when it is determined, the captain puts up a written notice, thus:--
Latitude, 44° 26'. Longitude, 16° 31'. Distance, 270.
The passengers, on seeing this notice, which is called a _bulletin_, know at once, from the first two items, whereabouts on the ocean they are; and from the last they learn that the distance which the ship has come since the day before is 270 miles.
This plan of finding out the ship's place every day, and of ascertaining the distance which she has sailed since the day before, would be perfectly successful, and amply sufficient for all the purposes required, if the sun could always be seen when the hour arrived for making the observation; but this is not the fact. The sky is often obscured by clouds for many days in succession; and, in fact, it sometimes happens that the captain has scarcely an opportunity to get a good observation during the whole voyage. There is, therefore, another way by which the navigator can determine where the ship is, and how fast she gets along on her voyage.
This second method consists of actually measuring the progress of the ship through the water, by an instrument called the log and line. The log--which, however, is not any log at all, but only a small piece of board, loaded at one edge so as to float upright in the water--has a long line attached to it, which line is wound upon a light windlass called a reel. The line, except a small portion of it at the beginning is marked off into lengths by small knots made in it at regular intervals. There are little rags of different forms and colors tied into these knots, so that they may easily be seen, and may also be distinguished one from the other.
When the time comes for performing the operation of _heaving the log_, as they call it, the men appointed for the purpose bring the log and the reel to the stern of the ship. One man holds the log, and another man the reel. There are two handles, one at each end of the reel, by which the man who serves it can hold it up over his head, and let the line run off from it. Besides the two men who hold the log and the reel, there is a third, who has a minute glass in his hand. The minute glass is like an hour glass, only there is but just sand enough in it to run a minute. The man who has the minute glass holds it upon its side at first, so as not to set the sand to running until all is ready.