[160] Page 68, line 30. Page 68, line 35. Ità coitio magnetica actus est magnetis, & ferri, non actio vnius.—See the introductory remarks to these notes. There is a passage in Scaliger's De Subtilitate ad Cardanum (Exercitat. CII., cap. 5, p. 156 op. citat.) which may be compared with Gilbert's for its use of Greek terms: "Nã cùm uita dicatur actus animæ, acceptus est abs te actus pro actione. Sed actus ille est ἐντελέχεια, nõ autem ἔργον. At Magnetis attractio est ἔργον, non autẽ ἐντελέχεια." To which Gilbert retorts: "non actio unius, utriusque ἐντελέχεια; non ἔργον, συνεντελέχεια et conactus potius quam sympathia." He returns on p. [70] to the attack on Scaliger's metaphysical notions. There is a parallel passage in the Epitome Naturalis Scientiæ of Daniel Sennert (Oxoniæ, 1664), in the chapter De Motu.
[161] Page 71, line 4. Page 71, line 8. vt in 8. physicorum Themistius existimat.—See Omnia Themistii Opera (Aldine edition, 1533, p. 63), Book 8 of his Paraphrase on Aristotle's Physica.
[162] Page 71, line 9. Page 71, line 14. Quod verò Fracastorius.—Op. citat., lib. i., cap. 7, p. 62 verso.
[163] Page 73, line 2. Page 73, line 2. si A borealis.—The editions of 1628 and 1633 omit the twelve words next following.
[164] Page 73, line 9. Page 73, line 11. ex minera.—Minera is not a recognized word, even in late Latin. It occurs again, p. [97], line 12.
[165] Page 77, line 2. Page 77, line 2. multo magis.—This is an à fortiori argument. It is interesting to find Gilbert comparing the velocity of propagation of magnetic forces in space with the velocity of light. The parallel is completed in line 13 by the consideration that as the rays of light require to fall upon an object in order that they may become visible, so the magnetic forces require a magnetic object in order to render their presence sensible.
[166] Page 78, line 14. Page 78, line 16. Orbem terrarum distinguunt.—The editions of 1628 and 1633 here add a figure of a globe marked with meridians and parallels of latitude, but with an erroneous versorium pointing to the south. These editions also both read existentiam for the word existentium in line 20.
[167] Page 83, line 5. Page 83, line 5. magnes longior maiora pondera ferri attollit.—Gilbert discovered the advantage, for an equal mass of loadstone, of an elongated shape. It is now well known that the specific amount of magnetism retained by elongated forms exceeds that in a short piece of the same material subjected to equal magnetizing forces.
[168] Page 83, line 24. Page 83, line 28. Non obstant crassa tabulata.—Gilbert has several times referred (e.g., on p. [77]) to the way in which magnetic forces penetrate solid bodies. The experimental investigation in this chapter
is the more interesting because it shows that Gilbert clearly perceived the shielding action of iron to be due to iron conducting aside or diverting the magnetic forces.