That in the production of steam heat is of incalculable value, there needs no proof. We derive special advantage from it, in the results of that machinery which astonish us by their magnitude, as well as by their elegance. Steam wafts us, in a few hours, from one extremity of the land to the other, and renders America, once called the New World, accessible in a few days.
Another instance of its application, often overlooked, is thus stated in the Quarterly Review:—“That extraordinary line of steam communication between England and her eastern possessions, (somewhat oddly called the overland journey,) of which Australia and New Zealand will hereafter form the extreme branches. The creation of the last twelve years, this communication has already acquired a sort of maturity of speed and exactness, notwithstanding the enormous distances traversed, and the changes necessary in transit from sea to sea. The Anglo-Indian mail in its two sections, and including passengers and correspondence, possesses a sort of individuality as the greatest and most singular line of intercourse on the globe. Two of the first nations of Europe, France and Austria, struggle for the privilege of carrying this mail across their territories. Traversing the length of the Mediterranean, it is received on the waters of the ancient Nile—Cairo and the Pyramids are passed in its onward course—the desert is traversed with a speed which mocks the old cavalcades of camels and loitering Arabs—it is re-embarked on the Red Sea, near a spot sacred in scriptural history—the promontory projecting from the heights of Mount Sinai, the shores of Mecca and Medina are passed in its rapid course down this great gulf—it emerges through the straits of Babelmandel into the Indian seas—to be distributed thence by different lines to all the great centres of Indian government and commerce, as well as to our more remote dependencies in the straits of Malacca and the Chinese seas. There is a certain majesty in the simple outline of a route like this, traversing the most ancient seats of empire, and what we are taught to regard as among the earliest abodes of man—and now ministering to the connexion of England with that great sovereignty she has conquered, or created, in the east; more wonderful, with one exception, than any of the empires of antiquity; and, perchance, also, more important to the general destinies of mankind.”
CHAPTER VIII.
The magic swan—Properties of the magnet—The mariners’ compass—The process of magnetizing—The dip of the needle—Magnetic properties in various substances.
A magician of former days had a figure of a swan, which floated on a vessel of water, round the rim of which were placed the twenty-four letters of the alphabet. Addressing the spectators, he was accustomed to ask for a name to be given him, and it was correctly spelt by the swan, as it moved from one letter to another till it had indicated the whole. A little philosophy, in this instance, produced repeatedly great astonishment. A magnetic bar was placed in the swan, and the performer had a powerful magnet concealed in his own dress, and the swan, of course, followed his motions. Thus, if he wanted the swan to spell “Selina,” he moved first to S, then to E, and so on, through the successive letters of that name, till the word was spelt. On one occasion, however, the performer was not a little disconcerted—the swan stopped in its course and refused to move. Again and again the effort was made, but it was utterly in vain; the magician could only acknowledge that some person was in the room aware of his secret, and counteracting his movements. Sir Francis Blake Delaval avowed himself to be the person: he produced a magnet which he had used on facing the performer as he stood at the table; the swan was, therefore, placed between two attractive instruments, and, of course, remained immovable.
A magnet may be described as a piece of iron, which possesses the property of turning towards the poles of the earth. This extraordinary quality does not necessarily belong to all specimens of iron in its native state, but only to one kind or variety called the oxide, on account of its union with oxygen in a particular condition. The possession of a special quality in this ore of iron was not discovered from its polarity, or power of turning to the poles of the earth, but from its property of attracting small pieces of iron, which are not magnetic; and hence it was called the loadstone.
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.
In addition to the properties already mentioned, the loadstone has the power of communicating its virtues to any piece of hard iron or steel, and that, without diminution of strength; so that, if but one piece had been discovered, it would have been sufficient for the production of all the magnets that have ever been formed by man. Other means may be adopted of accomplishing this purpose. Take a bar of iron, and, striking it several times with a hammer, it will become magnetic. This experiment may be performed with a common poker. The magnetism thus communicated to a steel bar will be much increased in power, if it be supported on another bar during the process of hammering.
Gay Lussac, a French chemist of great celebrity, discovered a method of making magnets by a process so simple, that it may, in all cases, be applied successfully. Take a piece of thin iron wire and suspend it in a vertical position. The earth itself being a magnet, induces a magnetic power in the wire. To render this permanent, twist the wire till it breaks, and a magnet will be obtained.