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. The Peregrinus’ Leyden manuscript (Fol. Cod. No. 227) already alluded to, Libri says (“Histoire des Sciences Mathém....” 1838, Vol. I. p. 383, note), is but a poor copy of the manuscript in the Paris Library (No. 7378A), from which latter the words _Petri ad Sygerum_ have been unfortunately transformed into _Petri Adsigerii_. He adds (Vol. II. pp. 70–71) that Humboldt cites (“Examen Critique,” p. 243) several authors who have alluded to the pretended Adsigerius. Mention is also made of the fact that W. Wenkebach, professor at the Hague Military School, examined the manuscripts in the Bodleian Library, Nos. 1629, 1794 and 2458, containing the treatise of Peregrinus, and that not one of them has the passage alluding to the declination. The Leyden manuscript, by the way, is said to be the only one, besides the Vatican copy, No. 5733, bearing the full date, which latter was first made known by Thévenot in his “Recueil de Voyages.” And it was a passage found in the Leyden manuscript (Q 27) which led to the belief that Peregrinus had first observed the variation or declination of the magnetic needle. The passage is as follows: “Take note that the magnet, as well as the needle that has been touched by it, does not point exactly to the poles, but that the part of it which is supposed to point to the South sometimes declines a little to the West, and that the part which looks towards the North sometimes inclines to the East. The exact quantity of this declination I have ascertained, after numerous experiments, to be five degrees. However, this declination is no obstacle to our guidance, because we make the needle itself decline from the true South by nearly one point and a half towards the West. A point contains five degrees.” This passage is unquestionably a late addition, being written in a different hand in a circle which itself is an incompleted outline of one of the figures of Peregrinus’ primitive compass.