On the Magnet, by William Gilbert

Chap. xii.

In what way Verticity exists in any Iron that has been smelted though not excited by a lodestone.

Working iron in a smithy.

H aving thus far211 demonstrated natural and inborn causes and powers acquired by means of the stone, we will now examine the causes of magnetick virtues in smelted iron that has not been excited by a stone. Loadstone and iron furnish and exhibit to us wonderful subtilities. It has been repeatedly shown above that iron not excited by a stone turns north and south; further that it has verticity, that is, special and peculiar polar distinctions, just as a loadstone, or iron which has been rubbed upon a loadstone. This indeed seemed to us at first wonderful and incredible; the metal of iron from the mine is smelted in the furnace; it runs out of the furnace, and hardens into a great mass; this mass is divided in great worksteads, and is drawn into iron bars, from which smiths again construct many instruments and necessary pieces of iron-work. Thus the same mass is variously worked up and transformed into very many similitudes. What is it, then, which preserves its verticity, and whence is it derived? So take this first from the above212 smithy. Let the blacksmith beat out upon his anvil a glowing mass of iron of two or three ounces weight into an iron spike of the length of a span of nine inches. Let the smith be standing with his face to the north, his back to the south, so that * the hot iron on being struck has a motion of extension to the north; and let him so complete his work with one or two heatings of the iron (if that be required); let him always, however, whilst he is striking the iron, direct and beat out the same point of it toward the north, and let him lay down that end toward the north. Let him in this way complete two, three, or more pieces of iron, nay, a hundred or four hundred; it is demonstrable that all those which are thus beaten out toward the north, and so placed whilst they are cooling, turn round on their centres; and floating pieces of iron (being transfixed, of course, through suitable corks) make a motion in the water, the determined end being toward the north. In the same way also pieces of iron acquire verticity from their direction whilst they are being beaten out and hammered or drawn out, * as iron wires are accustomed to do toward some point of the horizon between east and south or between south and west, or in the opposite direction. Those, however, which are pointed or drawn out rather toward the eastern or western point, conceive * hardly any verticity or a very undecided one. That verticity is especially acquired by being beaten out. But a somewhat inferior iron ore, in which no magnetick powers are apparent, if put in a * fire (its position being observed to be toward the poles of the world or of the earth) and heated for eight or ten hours, then cooled away from the fire, in the same position towards the poles, acquires a verticity in accordance with the position of its heating and cooling. Let a rod of cast iron be heated red-hot in a strong fire, in which it lies * meridionally (that is, along the path of a meridian circle), and let be removed from the fire and cooled, and let it return to its former temperature, remaining in the same position as before; then from this it will turn out that, if the same ends have been turned to the same poles of the earth, it will acquire verticity, and the end which looked toward the North on water with a cork before the heating, if it have been placed during the heating and cooling toward the fourth, now turns round to the south. But if perchance sometimes the rotation have been doubtful and somewhat feeble, let it be placed again in the fire, and when it is taken out at a red heat, let it be perfectly cooled toward the pole from which we desire the verticity, and the verticity will be acquired. Let the same rod be heated * in the contrary position, and let it be placed so at a red heat it is cool; for it is from its position in cooling (by the operation of the verticity of the earth) that verticity is put into the iron, and it turns round to parts contrary to its former verticity. So the end which formerly looked toward the north now turns to the south. In accordance with these reasonings and in these ways the boreal pole of the earth gives to the end of a piece of iron turned toward it a southern verticity, and that end is attracted by that pole. * And here it must be observed that this happens to iron not only when it is cooled in the plane of the horizon, but also at any angle to it almost up to the perpendicular toward the centre of the earth. So the heated iron conceives vigour and verticity from the earth more quickly in the course of its return to its normal state, and in its recovery, as it were (in the course of which it is transformed), than by its mere position alone. This is effected better and more * perfectly in winter and in colder air, when the metal returns more certainly to its natural temperature, than in summer and in warm regions. Let us see also what position alone and a direction toward the poles of the earth can effect by itself without fire and heat. Iron rods which have been placed and fixed for a long time, twenty * or more years, from south to north (as they not infrequently are fixed in buildings and across windows), those rods, I say, by that long lapse of time acquire verticity and turn round, whether hanging in the air, or floating (being placed on cork), to the pole toward which they were pointing, and magnetically attract and repel a balanced iron magnetick; for the long continued position of the body toward the poles is of much avail. This fact (although conspicuous by manifest experiments) is confirmed by an incident related in an Italian letter213 at the end of a book of Maestro Filippo Costa, of Mantua, Sopra le Compositioni degli Antidoti written in Italian, which translated runs thus: "A druggist of Mantua showed me a piece of iron entirely changed into a magnet, drawing another piece of iron in such a way that it could be compared with a loadstone. Now this piece of iron, when it had for a long time held up a brick ornament on the top of the tower of the church of St. Augustine at Rimini, had been at length bent by the force of the winds, and remained so for a period of ten years. When the monks wished to bend it back to its former shape, and had handed it over to a blacksmith, a surgeon named Maestro Giulio Caesare discovered that it was like a magnet and attracted iron." This was caused by the turning of its extremities toward the poles for so long a time. And so what has been laid down before about change of verticity should be borne in mind; how in fact the poles of iron spikes are altered, when a loadstone is placed against them only with its pole and points toward them, even at a rather long distance. Clearly it is in the same way that that large magnet also (to wit, the earth itself) affects a piece of iron and changes its verticity. For, although the iron may not touch the pole of the earth, nor any magnetick part of the earth, yet verticity is acquired and changed; not because the poles of the earth and the point itself which is 39° distant from our city of London, changes the verticity at a distance of so many miles; but because the whole magnetick earth, that which projects to a considerable height, and to which the iron is near, and that which is situated between us and the pole, and the vigour existing within the orbe of its magnetick virtue (the nature of the whole conspiring thereto), produces the verticity. For the magnetick effluence of the earth rules everywhere within the orbe of its virtue, and transforms bodies; but those things which are more similar to it, and specially connected with it by nature, it rules and controls; as loadstone and iron. Wherefore in very many matters of business and actions it is clearly not superstitious and idle to observe the positions and conditions of lands, the points of the horizon and the places of the stars. For as when a babe is brought forth into the light from its mother's womb, and acquires respiration and certain animal activities, then the planets and celestial bodies214, according to their position in the universe, and according to that configuration which they have with regard to the horizon and the earth, instil peculiar and individual qualities into the newly born; so that piece of iron, whilst it is being formed and lengthened out, is affected by the common cause (to wit, the earth); whilst it is returning also from its heated condition to its former temperature, it is imbued with a special verticity in accord with its position. Rather long pieces of iron sometimes have the same verticity * at each end; wherefore they have motions which are less certain and well ordered on account of their length and of the aforesaid processes, exactly as when an iron wire four feet long is rubbed at each end upon the same pole of a loadstone.

211 Page 139. There is a curious history to this picture of the blacksmith in his smithy striking the iron while it lies north and south, and so magnetizing it under the influence of the earth's magnetism. Woodcuts containing human figures are comparatively rare in English art of the sixteenth century; a notable exception being Foxe's Acts and Monuments with its many crude cuts of martyrdoms. The artist who prepared this cut of the smith took the design from an illustrated book of Fables by one Cornelius Kiliani or Cornelius van Kiel entitled Viridarium Moralis Philosophiæ, per Fabulas Animalibus brutis attributas traditæ, etc. (Coloniæ, 1594). This rare work, of which there is no copy in the British Museum, is illustrated by some 120 fine copper-plate etchings printed in the text. On p. 133 of this work is an etching to illustrate the fable Ferrarii fabri et canis, representing the smith smiting iron on the anvil, whilst his lazy dog sleeps beneath the bellows. The cut on p. 139 of Gilbert gives, as will be seen by a comparison of the pictures just the same general detail of forge and tools; but the position of the smith is reversed right for left, the dog is omitted, and the words Septrenio and Auster have been added.

Source engraving.

In the Stettin edition of 1628 the picture has again been turned into a copper-plate etching separately printed, is reversed back again left for right, while a compass-card is introduced in the corner to mark the north-south direction.

In the Stettin edition of 1633 the artist has gone back to Kiliani's original plate, and has re-etched the design very carefully, but reversing it all right for left. As in the London version of 1600, the dog is omitted, and the words Septentrio and Auster are added. Some of the original details — for example, the vice and one pair of pincers — are left out, but other details, for instance, the cracks in the blocks that support the water-tub, and the dress of the blacksmith, are rendered with slavish fidelity.

It is perhaps needless to remark that the twelve copper-plate etchings in the edition of 1628, and the twelve completely different ones in that of 1633, replace certain of the woodcuts of the folio of 1600. For example, take the woodcut on p. 203 of the 1600 edition, which represents a simple dipping-needle made by thrusting a versorium through a bit of cork and floating it, immersed, in a goblet of water. In the 1633 edition this appears, slightly reduced, as a small inserted copper-plate, with nothing added; but in the 1628 edition it is elaborated into a full-page plate (No. xi.) representing the interior, with shelves of books, of a library on the floor of which stands the goblet — apparently three feet high — with a globe and an armillary sphere; while beside the goblet, with his back to the spectator, is seated an aged man, reading, in a carved armchair. This figure and the view of the library are unquestionably copied — reversed — from a well-known plate in the work Le Diverse & Artificiose Machine of Agostino Ramelli (Paris, 1558).

In the Emblems of Jacob Cats (Alle de Wercken, Amsterdam, 1665, p. 65) is given an engraved plate of a smith's forge, which is also copied — omitting the smith — from Kiliani's Viridarium.

212 Page 140, line 2.. Page 140, line 2. præcedenti.— This is so spelled in all editions, though the sense requires præcedente.

213 Page 141, line 21. Page 141, line 24. quod in epistolâ quâdam Italicâ scribitur.— The tale told by Filippo Costa of Mantua about the magnetism acquired by the iron rod on the tower of the church of St. Augustine in Rimini is historical. The church was dedicated to St. John, but in the custody of the Augustinian monks. The following is the account of it given by Aldrovandi, Musæum Metallicum (1648, p. 134), on which page also two figures of it are given:

"Aliquando etiam ferrum suam mutat substantiam, dum in magnetem conuertitur, & hoc experientia constat, nam Arimini supra turrim templi S. Ioannis erat Crux a baculo ferreo ponderis centum librarum sustentata, quod tractu temporis adeò naturam Magnetis est adeptum, vt, illivs instar, ferrum traheret: hinc magna admiratione multi tenentur, qua ratione ferrum, quod est metallum in Magnetem, qui est lapis transmutari possit; Animaduertendum est id à maxima familiaritate & sympathia ferri, & magnetis dimanare cum Aristoteles in habentibus symbolum facilem transitum semper admiserit. Hoc in loco damus imaginem frusti ferri in Magnetem transmutati, quod clarissimo viro Vlyssi Aldrouando Iulius Caesar Moderatus diligens rerum naturalium inquisitor communicauit; erat hoc frustum ferri colore nigro, & ferrugineo, crusta exteriori quodammodo albicante." And further on p. 557.

"Preterea id manifestissimum est; quoniam Arimini, in templo Sancti Ioannis, fuit Crux ferrea, quæ tractu temporis in magnetem conuersa est, & ab vno latere ferrum trahebat, & ab altero respuebat." See also Sir T. Browne's Pseudodoxia Epidemica (edition of 1650, p. 48), and Boyle's tract, Experiments and Notes about the Mechanical Production of Magnetism (London, 1676, p. 12).

Another case is mentioned in Dr. Martin Lister's A Journey to Paris (Lond., 1699, p. 83). "He [Mr. Butterfield] shewed us a Loadstone sawed off that piece of the Iron Bar which held the Stones together at the very top of the Steeple of Chartres. This was a thick Crust of Rust, part of which was turned into a strong Loadstone, and had all the properties of a Stone dug out of the Mine. Mons. de la Hire has Printed a Memoir of it; also Mons. de Vallemont a Treatise. The very outward Rust had no Magnetic Virtue, but the inward had a strong one, as to take up a third part more than its weight unshod." Gassendi and Grimaldi have given other cases.

Other examples of iron acquiring strong permanent magnetism from the earth are not wanting. The following is from Sir W. Snow Harris's Rudimentary Magnetism (London, 1872, p. 10).

"In the Memoirs of the Academy of Sciences for 1731, we find an account of a large bell at Marseilles having an axis of iron: this axis rested on stone blocks, and threw off from time to time great quantities of rust, which, mixing with the particles of stone and the oil used to facilitate the motion, became conglomerated into a hardened mass: this mass had all the properties of the native magnet. The bell is supposed to have been in the same position for 400 years."

214 Page 142, line 13. Page 142, line 15. tunc planetæ & corpora cœlestia.— Gilbert's extraordinary detachment from all metaphysical and ultra-physical explanations of physical facts, and his continual appeal to the test of experimental evidence, enabled him to lift the science of the magnet out of the slough of the dark ages. This passage, however, reveals that he still gave credence to the nativities of judicial Astrology, and to the supposed influence of the planets on human destiny.

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Last updated Friday, March 14, 2014 at 22:17