Bibliographical history of electricity & magnetism, chronologically arranged

by Unknown

Chap. I states that the intention or object of the work is to make known the hitherto hidden nature, occult properties, of the loadstone, the art of treating the latter, the making of scientific instruments, and matters of interest to students of nature, astrologers and sailors.

Chap. II. The investigator in this line should know the natures of things and understand the motions of the heavenly bodies, but, above all, he should be assiduous in handiwork for experimental research.

Chap. III indicates four different requisite qualities of the loadstone, and tells where they are to be found and how to select and test them—the best of them being free from flaws, of great density and of a bluish or celestial colour.

Chap. IV shows how to find in the loadstone the two poles, one north and the other south, using preferably a globular magnet,[17] placing thereon a needle or an oblong piece of iron, and, either drawing lines in the direction taken by the needle, so that they “may meet at two points, just as all the meridian circles of the world meet at the two opposite poles of the world,” or, by merely marking the magnet so that “the opposite points will be correctly placed just as are the poles in a sphere.”

Chap. V. In order to find the poles in a stone—which of them is the North and which the South—take a round wooden vessel shaped like a skiff (paropsidis, parascidis), and place the stone therein, then put the vessel containing the stone into another large vessel filled with water, so that the first-named vessel may float into the larger one: “The stone in the first vessel will be like a sailor in a ship, and the first vessel may float roomily into the second as does a ship in a river, and the stone so placed will turn its small vessel acting as the Northern pole in the direction of the Northern heaven.... If this pole were then turned away a thousand times, a thousand times would it return to its place by the will of God.”

Chap. VI. Having found which pole is the Northern, mark it so that it may be known when necessary. Place the stone into a small vessel, as shown in Chap. V, then hold another stone in the hand and approach its Northern part to the Southern part of the stone floating in the vessel, and the floating stone will follow the other “as if it wished to adhere thereto.... Know that, as a rule, the Northern part of one stone attracts the Southern part of another stone and the Southern the Northern.”

Chap. VII. When the needle or oblong piece of iron (alluded to in Chap. IV) has touched the magnet and been attached to a light piece of wood or stalk and then placed in a vessel of water, one part will be turned towards the mariner’s star because it is near the pole, “the fact being that it does not turn towards the aforesaid star but towards the pole.” That end of the iron which has touched the Southern end of the stone turns towards the Northern quarter of the sky, and vice versa.

Chap. VIII. If you wish to attract iron floating on water, hold the Southern part of a loadstone to the Northern part of the iron and the iron will follow. But, if you bring the North end of the stone near the North end of the iron, the latter will avoid the stone. “If, however, violence is used towards the ends, so that, for instance, the Southern end of the iron which was touched with the Northern end of the magnet is now touched with the Southern end of the magnet ... the power in the iron will easily be changed, and that will become Southern which was previously Northern, and the converse.”

Chap. IX. “The Northern part of the magnet attracts the Southern and the reverse, as has been shown; in which attraction the magnet is an ‘agent’ of greater power while the ‘patient’ (i. e. the other which is acted upon) is, of weaker.” This is proved by taking a loadstone—marking it, for instance, AD—dividing, separating it into two parts, and placing one part (the Northern, marked A, called the “agent”) into water so that it will float. It will turn “to the North, as before, for the division does not deprive the parts of the stone of their properties, if it be homogeneous.” The other part (the Southern, marked D, called the “patient”) is next to be floated in a similar manner. When this is done, the other ends of the two stones should be marked respectively B and C. It will then be observed that “if the same parts are again brought near each other, one will attract the other, so that they will be joined together again at B and C where the division took place. Whence it is that they become one body with the same natural propensity as at first. The proof of this is that if they are joined together they will possess the same oppositions (opposite poles) they first contained. The ‘agent,’ therefore, as you will see by experiment, intends to unite its ‘patient’ to itself, and this takes place on account of the similitude between them.... And, in the same way, it will happen that if A is joined with D, the two lines will become one, by virtue of that very attraction, in this order CD—AB ... there will then remain the identity of the extreme parts as at first, before they were reunited, for C will be the North point and B the South point, as B and C were before.... It is therefore evident, from these observations, why the Southern parts do attract the Northern, and the reverse, and why the attraction of the South by the South, and the North by the North, is not according to Nature.”

Chap. X. “Some weak inquirers have imagined that the power which the magnet exercises over iron lies in those mineral places in which the magnet is found ... but it is found in different parts of the world.... Besides, when iron or the magnet turns towards the Southern as well as to the Northern quarter, as is evident from what has already been said, we are compelled to decide that the attraction is exercised on the poles of the magnet not only from the locality of its quarry, from which ensues the evident result that, wheresoever a man may be, the direction of this stone appears to his eye, according to the position of his meridian circle. All the meridian circles, however, meet together at the poles of the globe, wherefore it is that the poles of the magnet receive their power from the poles of the world. From this, it manifestly appears that the direction of the magnet is not towards the mariner’s star, as the meridian circles do not meet there, but all the poles, for the mariner’s star is always found beyond the meridian circle of any region unless it be twice in a complete revolution of the firmament. Likewise from this, it is manifest that the parts of the magnet receive their power from the world’s poles ... the whole magnet from the whole heavens.”[18] Then follows a suggestive experiment looking towards perpetual motion, by which one may secure “a wonderful secret” and even “be saved the trouble of having any clock.” Here, it is given that a terrella, poised on its poles in the meridian, moves circularly with a complete revolution in twenty-four hours. This is explained by N. Cabæus in his “Phil. Magn.,” lib. iii. cap. 4.