Part II
Chap. I. He takes a round, or an ovoid magnet, and, after noting its poles, files it between the two poles on both sides so that it may be like a compressed sphere and thus occupy less space. He then encloses this magnet between two light wooden capsules, or boxes (cassulas) after the manner of a mirror ... so fastened (with glue) that they cannot be opened and water cannot enter. Then, says he, “place the capsules thus adjusted in a large vessel full of water in which the two quarters of the globe, viz. the South and the North, are found and marked, and let them be indicated by a thread extending from the Northern to the Southern part of the vessel; allow the capsules, or boxes, to float and let there be above them a slender piece of wood in the form (position) of a diameter. Then move this piece of wood above the boxes until it is equidistant from the meridianal line previously found and indicated by the thread, or is the same (line) itself. This being done, according to the piece of wood so situated, draw a line on the capsules, or boxes, and it will be the perpetual meridianal line in all countries. That line, therefore, when cut at right angles by another will be divided in the centre and will be the line of the East and West. You will thus have four quadrants actually marked on the capsules, or boxes, representing the four quarters of the globe, of which each will be divided into ninety, so that there may be in the universe CCCLX parts (degrees) in the entire circumference of the capsules, or boxes. Inscribe divisions on it as they were formerly inscribed on the back of the astrolabe. There should be, besides, a slender and light ruler above the capsules so inscribed after the manner of the ruler on the back of the astrolabe. Instead, however, of the sights (pinnularum), should be erected at right angles two pins over the ends of the ruler.”
This floating compass and the pivoted compass described in the following chapter are to be found illustrated, pp. 67–77, figs. 10 and 12, at end of Part II of Bertelli Barnabita’s Memoirs above referred to.
Chap. II. For the construction of a “better instrument and of more certain effects” (the pivoted compass) he says: “Let there be made a vessel of wood, brass or any other solid material that you desire, and let it be turned in the shape of a jar (pixidis tornatum) somewhat deep and tolerably large and let a cover of transparent material, such as glass or crystal, be fitted to it. If the whole vessel were of transparent substance so much the better. Let there be placed in the centre of the same vessel a slender axis of brass or silver, applying its extremities to the two parts of the jar, that is to say (to the) higher and lower. Let two holes be then made in the centre of the axis facing each other at right angles. Then let a piece of iron wire, like a needle, be passed through one of these holes and another wire of silver or brass be passed through the other, intersecting the iron at right angles. Let the cover at first be divided into quadrants and each of the quadrants into ninety parts, as was taught regarding the other instrument. Let North and South and East and West be marked on it and let a rule of transparent material be added to it with wires set upright at the ends. You will approach what part of the magnet you please, whether North or South, to the crystal until the needle moves towards it and receives virtue from it. When this is done, turn the vessel until one end (of the needle) stands directly over the North in the instrument coinciding with the Northern quarter of the sky. This being done, turn the rule to the sun, by day, and to the stars, by night, in manner above indicated. By means of this instrument, you will be enabled to direct your footsteps to states and islands and to any places on the globe, and wheresoever you may be, whether on land or on sea, so long as their latitudes and longitudes are known to you.”
Chap. III. He constructs “a wheel which shall be constantly in motion,” by making a very thin concave, silver case, after the manner of a mirror, suitably perforated, around the rim of which he inserts small iron nails, or teeth, bent closely toward each other and which he then places upon an immovable axis so that it may revolve easily.” He continues: “Let a silver wire be added to this axis, fixed to it and placed between two bowls on the end of which let a magnet be set, prepared in this manner. Let it be rounded and its poles ascertained, as before indicated; afterwards, let it be fashioned in the shape of an egg with the poles intact, and let it be somewhat filed down in two intermediate and opposite parts with the object of its being compressed and occupying less space so that it may not touch the inner walls ... let the magnet be placed on the wire ... and let the North pole be somewhat inclined towards the small teeth of the wheel so that it may exercise its power ... so that each tooth shall arrive at the North pole and, owing to the impetus of the wheel, shall pass it by and approach the Southern quarter. Thus every small tooth will be in a perpetual state of attraction and avoidance. And, in order that the wheel may perform its duty with greater rapidity, insert, between the cases, a small round brass or silver pebble of such size that it may be caught between any two of the small teeth, so that, as one part of the wheel comes uppermost, the pebble may fall to the opposite part. Wherefore, whilst the motion of the wheel is perpetual on one side, the same will be in the case of the pebble on the other side, or the fall of the pebble caught between any two of the teeth will be perpetual to the opposite side because as it is drawn towards the centre of the earth by its weight, it assists the motion by not suffering the small teeth to remain at rest in front of the stone. Let there be spaces, however, between the small teeth conveniently curved, so as to catch the pebble as it falls in the way the present description indicates.”
Petrus Peregrinus. Facsimile of a Ms. at the Bodleian Library, of the “Epistola de Magnete,” wherein is described the earliest known pivoted compass.
Gilbert alludes to this perpetual-motion engine as having been devised or delineated by Peregrinus after he had got the idea from others (“De Magnete,” Book II. chap. xxxv.), and says that Jerome Cardan writes (“Opera,” Batav., 1663; “De Rerum Varietate,” Book, IX. chap. xlviii.) he could construct one out of iron and loadstone—not that he ever saw such a machine; that he merely offers the idea as an opinion and quotes from a report of the physician Antonio de Fantis of Treviso published in “Tabula generalis ac mare magnum scotice subtilitatis....”
In the “Magisterium Naturæ et Artis,” P. Francisci Tertii de Lanis, Brixiæ, 1684, Tractatus Tertius, Caput Secundum, p. 489, under Problema, I, Motus perpetuus magnetis, will be found allusion to the machines of (1) P. Peregrinus, as described in his epistle; (2) Taisnier; (3) Ant. de Fantis (cited by Cardan, as stated above); also mention of those of P. Schottus, Athan. Kircherus, Hieronimus Finugius and others; the most important of these being again alluded to throughout the third chapter of the same tract.
Gilbert makes further allusion to P. Peregrinus in his Book I. chap. i.; Book II. chap. xxxv.; Book III. chap. i.; Book IV. chap. i.; Book VI. chap. iv.