There are many uses to which the magnet has been applied, and there is a probability of its being much more extensively employed; but its most important application is in the construction of the mariners’ compass, which renders it possible freely to traverse the ocean. There has been some controversy as to the discovery of the directive power of the magnet, and the invention of the compass. It was once supposed to have been unknown until about the thirteenth century, but it is now generally acknowledged that the Chinese were acquainted with the compass at least eleven hundred and fourteen years before the birth of Christ. At the commencement of the thirteenth century, it was certainly in use in Europe; for cardinal de Vitty mentions it with some particularity, in a work entitled “The History of the East,” where he says, “The iron needle, after contact with the loadstone, constantly turns to the north star, which, as the axis of the firmament, remains immovable, while the others revolve; and hence it is essentially necessary to those navigating on the ocean.” This shows that the compass was not invented in Europe, as commonly believed, by Gioia, a pilot, and a native of Pasitano, a small village, situated near Amalfi, who lived about the end of the thirteenth century, but, by him, it appears to have been made fully available for the purposes of navigation. As used by sailors in the Mediterranean at that period, it was a very uncertain guide; for the compass then consisted of a magnetic needle attached to two straws on a piece of cork, floating on water in a basin, or glass vase. Gioia, therefore, placed the magnetic needle upon a pivot, so that it was free to move in any direction, and thus prevented that inconvenience and inaccuracy of observation which must have resulted from the motion of the needle floating on water, agitated by the tossing of the vessel. The magnetic needle was afterwards attached to a card divided into thirty-two points, called the _rose des vents_, so that the direction in which a vessel was sailing could be minutely determined, and the means of ascertaining it was no longer dependent on the accuracy of the eye in measuring distances. The mariners’ compass is still constructed in the same manner, but is inclosed in a box with a glass cover, and is thus preserved from the influence of the wind. Another improvement has been made in so suspending the box that, however the vessel may be pitched by the waves, and rolled from side to side, the needle remains in a horizontal position, and gives accurate indications of the direction in which the vessel is sailing.