[138] PAGE 54, LINE 16. Page 54, line 18. _Gemma Vincentij rupis._--See the note to p. 48 _supra_, where the name _Vincentina_ occurs.

[139] PAGE 54, LINE 30. Page 54, line 35. _orobi._--The editions of 1628 and 1633 read _oribi_.

[140] PAGE 55, LINE 34. Page 55, line 42. _in euacuati._--The editions of 1628 and 1633 read _inevacuati_.

[141] PAGE 58, LINE 21. Page 58, line 25. _assurgentem vndam ... declinat ab F._--These words are wanting in the Stettin editions.

[142] PAGE 59, LINE 9. Page 59, line 9. _fluore._--This word is conjectured to be a misprint for _fluxu_ but it stands in all editions.

[143] PAGE 59, LINE 22. Page 59, line 25. _Ruunt ad electria._--This appears to be a slip for _electrica_, which is the reading of the editions of 1628 and 1633.

[144] PAGE 60, LINE 7. Page 60, line 9. _tan[=q] materiales radij._--The suggestion here of material _rays_ as the _modus operandi_ of electric forces seems to foreshadow the notion of electric lines of force.

[145] PAGE 60, LINE 10. Page 60, line 12. _Differentia inter magnetica & electrica._--Though Gilbert was the first systematically to explore the differences that exist between the magnetic attraction of iron and the electric attraction of all light substances, the point had not passed unheeded, for we find St. Augustine, in the _De Civitate Dei_, liber xxi., cap. 6, raising the question why the loadstone which attracts iron should refuse to move straws. The many analogies between electric and magnetic phenomena had led many experimenters to speculate on the possibility of some connexion between electricity and magnetism. See, for example, Tiberius Cavallo, _A Treatise on Magnetism_, London, 1787, p. 126. Also the three volumes of J. H. van Swinden, _Receuil de Memoires sur l'Analogie de Electricite et du Magnetisme_, La Haye, 1784. Aepinus wrote a treatise on the subject, entitled _De Similitudine vis electricae et magneticae_ (Petropolis, 1758). This was, of course, long prior to the discovery, by Oersted, in 1820, of the real connexion between magnetism and the electric current.

[146] PAGE 60, LINE 25. Page 60, line 31. _Coitionem dicimus, non attractionem._--See the remarks, at the outset of these Notes, on Gilbert's definitions of words.

[147] PAGE 60, LINE 33. Page 61, line 1. _Orpheus in suis carminibus._--This passage is in the chapter [Greek: Lithika] of Orpheus, verses 301 to 327. See Note to p. 11, line 19.

[148] PAGE 61, LINE 15. Page 61, line 19. _Platonis in Timaeo opinio_.--The passage runs (edition Didot, vol. ii., p. 240, or Stephanus, p. 80, C.):

[Greek: Kai de kai ta ton hudaton panta rheumata eti de ta ton keraunon ptomata kai ta thaumazomena elektron peri tes helxeos kai ton Herakleion lithon, panton touton holke men ouk estin oudeni pote, to de kenon einai meden periothein te hauta tauta eis allela, to te diakrinomena kai sunkrinomena pros ten hauton diameibomena hedran hekasta ienai panta, toutois tois pathemasi pros allela sumplechtheisi tethaumatourgemena toi kata tropon zetounti phanesetai.]

[149] PAGE 61, LINE 30. Page 61, line 38. The English version of the lines of Lucretius is from Busby's translation.

[150] PAGE 62, LINE 5. {45} Page 62, line 7. _Iohannes Costaeus Laudensis._--Joannes Costa, of Lodi, edited Galen and Avicenna. He also wrote a _De universali stirpium Natura_ (Aug. Taurin., 1578).

[151] PAGE 63, LINE 3. Page 63, line 4. _Cornelius Gemma 10.

Cosmocrit._--This refers to the work _De Naturae Divinis Characterismis ...

Libri ii. Avctore D. Corn. Gemma_ (Antv., 1575, lib. i., cap. vii., p.

123).

"Certe vt a magnete insensiles radij ferrum ad se attrahunt, ab echineide paruo pisciculo sistuntur plena nauigia, a catoblepa spiritu non homines solum, sed & alta serpentum genera interimuntur, & saxa dehiscunt."

See also Kircher's _Magneticum Naturae Regnum_ (Amsterodami, 1667, p. 172), Sectio iv., cap. iii., De Magnete Navium, quae Remora seu Echeneis dicitur.

See the note to p. 7, line 21.

[152] PAGE 63, LINE 6. Page 63, line 7. _Guilielmus Puteanus._--Puteanus (Du Puys) wrote a work _De Medicamentorum quomodocunque Purgantium Facultatibus_, Libri ii. (Lugd., 1552), in which he talks vaguely about the substantial "form" of the magnet, and quotes Aristotle and Galen.

[153] PAGE 63, LINE 21. Page 63, line 25. _Baptistae Portae._--The passage in the translation is quoted from the English version of 1658, pp. 191, 192.

[154] PAGE 64, LINE 4. Page 64, line 9. _Erudite magis Scaliger._--Gilbert pokes fun at Scaliger, whose "erudite" guess (that the motion of iron to the magnet was that of the offspring toward the parent) is to be found in his book _De Subtilitate, ad Cardanum_, Exercitatio CII. (Lutetiae, 1557, p.

156 _bis_).

[155] PAGE 64, LINE 7. Page 64, line 11. _Diuus Thomas._--On p. 3 Gilbert had already spoken of St. Thomas Aquinas as a man of intellect who would have added more about the magnet had he been more conversant with experiments. The passage here quoted is from the middle of Liber vii. of his commentaries on the _de Physica_ of Aristotle, _Expositio Diui Thome Aquinatis Doctoris Angelici super octo libros Physicorum Aristotelis_, etc.

(Venice, Giunta edition, 1539, p. 96 _verso_, col. 2).

[156] PAGE 64, LINE 16. Page 64, line 24. _Cardinalis etiam Cusanus._--Cardinal de Cusa (Nicolas Khrypffs) wrote a set of dialogues on Statics, _Nicolai Cusani de staticis experimentis dialogus_ (1550), of which an English version appeared in London in 1650 with the title, _The Idiot in four books; the first and second of wisdom, the third of the minde, the fourth of statick experiments. By the famous and learned C.

Cusanus._ In the fourth book _of statick Experiments, Or experiments of the Ballance_, occurs (p. 186) the following:

"_Orat._ Tell me, if thou hast any device whereby the vertues of stones may be weighed.

"_Id._ I thinke the vertue of the Load-stone might be weighed, if putting some Iron in one scale, and a Load-stone in the other, untill the ballance were even, then taking away the Load-stone, and some other thing of the same weight being put into the scale, the Load-stone were holden over the Iron, so that that scale wou'd begin to rise; by reason of the Load-stones attraction of the Iron, then take out some of the weight of the other scale, untill the scale wherein the iron is, doe sinke againe to the aequilibrium, or equality still holding the Load-stone unmovable as it was; I beleeve that by weight of what was taken out of the contrary scale, one might come proportionably to the weight of the vertue or power of the Load-stone. And in like manner, the vertue of a Diamond, might be found hereby, because {46} they say it hinders the Load-stone from drawing of Iron; and so other vertues of other stones, consideration, being alwayes had of the greatnesse of the bodyes, because in a greater body, there is a greater power and vertue."

In the 1588 edition of Baptista Porta's _Magiae Naturalis Libri xx._, in lib. vii., cap. xviii., occurs the description of the use of the balance to which Gilbert refers.

[157] PAGE 67, LINE 21. Page 67, line 22. _aeris rigore._--All editions read thus, but the sense seems to require _frigore_.

[158] PAGE 67, LINE 27. Page 67, line 31. _Fracastorius._--See his _De Sympathia_, lib. i., cap. 5 (Giunta edition, 1574, p. 60).

[159] PAGE 68, LINE 5. Page 68, line 6. _Thaletis Milesij._--See the note to p. 11, line 26.

[160] PAGE 68, LINE 30. Page 68, line 35. _Ita 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: "N cum uita dicatur actus animae, acceptus est abs te actus pro actione. Sed actus ille est [Greek: entelecheia], n autem [Greek: ergon]. At Magnetis attractio est [Greek: ergon], non aut[~e] [Greek: entelecheia]." To which Gilbert retorts: "non actio unius, utriusque [Greek: entelecheia]; non [Greek: ergon], [Greek: sunentelecheia] 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 Scientiae_ of Daniel Sennert (Oxoniae, 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 ver 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 _a 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 {47} 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.

[169] PAGE 85, LINE 26. Page 85, line 31. _non conveniant._--The editions of 1628 and 1633 both read _et conveniant_.

[170] PAGE 86, LINE 3. Page 86, line 3. _illud quod exhalat._--Literally, _that which exhales_, in the sense of that which escapes: but in modern English the verb exhale in the active voice is now not used of the substance that escapes, but is used of the thing which emits it. It must therefore be rendered _that which is exhaled_ (_i.e._, breathed out).

[171] PAGE 86, LINE 13. Page 86, line 15. _Ita tota interposita moles terrestris._--Gilbert's notion that the gravitational force of the moon in producing the tides acts _through_ the substance of the earth may seem curiously expressed. But the underlying contention is essentially true to-day. The force of gravity is not cut off or screened off by the interposition of other masses. A recent investigation by Professor Poynting, F.R.S., has shown that so far as all evidence goes all bodies, even the densest, are transparent with respect to gravitational forces.

[172] PAGE 86, LINE 18. Page 86, line 20. _Sed de aestus ratione alias._--There is no further discussion of the tides in _De Magnete_. But a short account is to be found in Gilbert's posthumous work _De Mundo nostro Sublunari Philosophia nova_ (Amsterdam, Elzevir, 1651), in Lib. v., the part which in the manuscript was left in English, and was turned into Latin by his brother. It comprises about fifteen quarto pages, from Cap. X. to Cap. XIX. inclusive, beginning with a characteristic diatribe against Taisnier, Levinus Lemnius, and Scaliger. But in assigning causes he himself goes wide of the mark. Proceeding by a process of elimination he first shows that the moon's light cannot be the cause that impels the tides.

"Luna," he says, "non radio, non lumine, maria impellit. quomodo igitur?

Sane corporum conspiratione, acque (ut similitudine rem exponam) Magnetica attractione." This cryptic utterance he proceeds to explain by a diagram, and adds: "Quare Luna non tam attrahit mare, quam humorem & spiritum subterraneum; nec plus resistit interposita terra, quam mensa, aut quicquam aliud densum, aut crassum, magnetis viribus."

[173] PAGE 87, LINE 7. Page 87, line 9. _armatura._--Here this means the cap or snout of iron with which the loadstone was armed. This is apparently the first use of the term in this sense.

In the _Dialogues of Galileo_ (p. 369 of Salusbury's _Mathematical Collections_, Dialogue iii.), Sagredus and Salviatus discuss the arming of the loadstone, and the increased lifting power conferred by adding an iron cap. Salviatus mentions a loadstone in the Florentine Academy which, unarmed, weighed six ounces, lifting only two ounces, but which when armed took up 160 ounces. Whereupon Galileo makes Salviatus say: "I extreamly praise, admire, and envy this Authour, for that a conceit so stupendious should come into his minde. ... I think him [_i.e._, Gilbert] moreover worthy of extraordinary applause for the many new and true Observations that he made, to the disgrace of so many fabulous Authours, that write not only what they do not know, but whatever they hear spoken by the foolish vulgar, never seeking to assure themselves of the same by experience, perhaps, because they are unwilling to diminish the bulk of their Books."

[174] PAGE 87, LINE 12. Page 87, line 15. The reference to _lib._ 3 is {48} a misprint for _lib._ 2. It is corrected in the edition of 1633, but not in that of 1628.

[175] PAGE 87, LINE 17. Page 87, line 21. _conactu._--The editions of 1628 and 1633 read _conatu_.