“I neither wish to bring it about nor do I desire to witness it; but should it come to pass through the force of public opinion, I would second it to the full extent of my power. In such a case you will hear me spoken of. Adieu. I shall depart to-morrow; but pray leave me now, and let me have a little sleep.”
Count du Saillant left the room without saying another word. Very early on the following morning Mirabeau was on his way to Paris.
Terrestrial Magnetism. (From Chambers's Edinburgh Journal.)
It is proposed in the following article to give the reader some idea of one of the greatest and most extensive scientific works going on at the present time in this country—namely, the examination of the phenomenon of the earth's [pg 652] magnetism; but before doing so, it will be necessary to make a few prefatory observations respecting magnetism generally.
The attractive power of the natural magnet or loadstone over fragments of iron seems to have been known from the remotest antiquity. It is distinctly referred to by ancient writers, and Pliny mentions a chain of iron rings suspended from one another, the first being upheld by a loadstone. It is singular that although the common properties of the loadstone were known, and even studied, during the dark ages, its directive power, or that of a needle touched or rubbed by it, seems to be the discovery of modern times, notwithstanding the claims of the Chinese and Arabians to an early acquaintance with this peculiarity.
There is no doubt that the mariner's compass was known in the twelfth century, for several authors of that period make special allusion to it; but centuries elapsed before its variation from pointing precisely to the poles became noticed. If a magnet be suspended by a thread, in such a manner as to enable it to move freely, it will, when all other magnetic bodies are entirely removed from it, settle in a fixed position, which, in this country, is about 25° to the west of north; this deviation of the needle from the north is called its variation. Again, if, in place of suspending a magnetized needle, making it move horizontally on a pivot, we balance it upon a horizontal axis, as the beam of a pair of scales, we shall find that it no longer remains horizontal, but that one end will incline downward, or, as it is called, dip, and this dip or inclination from a horizontal line is about 70° in this country.
Thus we are presented with two distinct magnetical phenomena: 1. The variation or declination of the needle; 2. Its dip or inclination; and to these we may add the intensity or force which draws the needle from pointing to the north, and which varies in different latitudes. These phenomena constitute what has been called terrestrial magnetism.
Recent writers, and among them the great philosopher Humboldt, have shown that in all probability the declination or variation of the magnet was known as early as the twelfth century; but this important discovery has been generally ascribed to Columbus. His son Ferdinand states that on the 14th September 1492, his father, when about 200 leagues from the island of Ferro, noticed for the first time the variation of the needle. “A phenomenon,” says Washington Irving, “that had never before been remarked.” “He perceived,” adds this author, “about nightfall that the needle, instead of pointing to the north star, varied half a point, or between five and six degrees, to the northwest, and still more on the following morning. Struck with this circumstance, he observed it attentively for three days, and found that the variation increased as he advanced. He at first made no mention of this phenomenon, knowing how ready his people were to take alarm; but it soon attracted the attention of the pilots, and filled them with consternation. It seemed as if the laws of nature were changing as they advanced, and that they were entering another world, subject to unknown influences. They apprehended that the compass was about to lose its mysterious virtues; and without this guide, what was to become of them in a vast and trackless ocean? Columbus tasked his science and ingenuity for reasons with which to allay their terrors. He told them that the direction of the needle was not the polar star, but to some fixed and invisible point: the variation was not caused by any failing in the compass, but because this point, like the heavenly bodies, had its changes and revolutions, and every day described a circle round the pole. The high opinion that the pilots entertained of Columbus as a profound astronomer gave weight to his theory, and their alarm subsided.”
Thus, although it is possible that the variation of the needle had been noticed before the time of Columbus, it is evident that he had discovered the amount of the variation, and that it varied in different latitudes. The great philosopher Humboldt observes on this point, that “Columbus has not only the incontestible merit of having first discovered a line without magnetic variation, but also of having, by his considerations on the progressive increase of westerly declination in receding from that line, given the first impulse to the study of terrestrial magnetism in Europe.”