In the English translation of Solinus's _De Mirabilibus_ (_The excellent and pleasant worke of Julius Solinus containing the noble actions of humaine creatures, the secretes and providence of nature, the descriptions of countries ... tr. by A. Golding, gent._, Lond., 1587), chapter xv. on Arabia has the following:

"Hee findeth likewise the Iris in the Red sea, sixe cornered as the Crystall: which beeing touched with the Sunnebeames, casteth out of him a bryght reflexion of the ayre like the Raynebowe."

Iris is also mentioned by Albertus Magnus (_De mineralibus_, Venet., 1542, p. 189), by Marbodeus Gallus (_De lapidibus_, Par. 1531, p. 78), who describes it as "crystallo simulem sexangulam," by Lomatius (_Artes of curious Paintinge_, Haydocke's translation, Lond., 1598, p. 157), who says, "... the Sunne, which casting his beames vpon the _stone Iris_, causeth the _raine-bowe_ to appeare therein ...," and by "Sir" John Hill (_A General Natural History_, Lond., 1748, p. 179).

Figures of the Iris given by Aldrovandi in the _Musaeum Metallicum_ clearly depict crystals of quartz.

[120] PAGE 48, LINE 16. Page 48, line 18. _Vincentina, & Bristolla (Anglica gemma siue fluor)_. This is doubtless the same substance as the _Gemma Vincentij rupis_ mentioned on p. 54, line 16 (p. 54, line 18, of English Version), and is nothing else than the so-called "Bristol diamond," a variety of dark quartz crystallized in small brilliant crystals upon a basis of haematite. To the work by Dr. Thomas Venner (Lond., 1650), entitled _Via Recta_ or the _Bathes of Bathe_, there is added an appendix, _A Censure concerning the water of Saint Vincents Rocks neer Bristol (Urbs pulchra et Emporium celebre)_, in which, at p. 376, occurs this passage: "This Water of Saint _Vincents_ Rock is of a very pure, cleare, crystalline substance, answering to those crystalline Diamonds and transparent stones that are plentifully found in those Clifts."

In the _Fossils Arranged_ of "Sir" John Hill (Lond., 1771), p. 123, is the following entry: "Black crystal. Small very hard heavy glossy. Perfectly black, opake. Bristol (grottos, glass)" referring to its use.

The name _Vincentina_ is not known as occurring in any mineralogical book.

Prof. H. A. Miers, F.R.S., writes concerning the passage: "_Anglica gemma sive fluor_ seems to be a synonym for _Bristolla_, or possibly for _Vincentina et Bristolla_. Both quartz and fluor are found at Clifton. In that case Vincentina and Bristolla refer to these two minerals, and if so one would expect Bristolla to be the Bristol Diamond, and Vincentina to be the comparatively rare Fluor spar from that locality."

At the end of the edition of 1653 of Sir Hugh Plat's _Jewel House of Art and Nature_, is appended _A rare and excellent Discourse of Minerals, Stones, Gums, and Rosins; with the vertues and use thereof_, By D. B.

_Gent_. Here, p. 218, we read:

"We have in England a stone or mineral called a Bristol stone (because {41} many are found thereabouts) which much resembles the Adamant or Diamond, which is brought out of Arabia and Cyprus; but as it is wanting of the same hardnesse, so falls it short of the like vertues."

[121] PAGE 48, LINE 18. Page 48, line 19. _Crystallus._--Rock-crystal.

Quartz. Pliny's account of it (Philemon Holland's version of 1601, p. 604) in book xxxvii., chap, ii., is:

"As touching Crystall, it proceedeth of a contrarie cause, namely of cold; for a liquor it is congealed by extreame frost in manner of yce; and for proofe hereof, you shall find crystall in no place els but where the winter snow is frozen hard: so as we may boldly say, it is verie yce and nothing else, whereupon the Greeks have give it the right name Crystallos, _i._ Yce.... Thus much I dare my selfe avouch, that crystall groweth within certaine rockes upon the Alps, and these so steepe and inaccessible, that for the most part they are constrained to hang by ropes that shall get it forth."

[122] PAGE 48, LINE 18. Page 48, line 20. _Similes etiam attrahendi vires habere videntur vitrum ... sulphur, mastix, & cera dura sigillaris._ If, as shown above, the electric powers of diamond and ruby had already been observed, yet Gilbert was the first beyond question to extend the list of _electrics_ beyond the class of precious stones, and his discovery that _glass_, _sulphur_, and _sealing-wax_ acted, when rubbed, like amber, was of capital importance. Though he did not pursue the discovery into mechanical contrivances, he left the means of that extension to his followers. To Otto von Guericke we owe the application of sulphur to make the first electrical machine out of a revolving globe; to Sir Isaac Newton the suggestion of glass as affording a more mechanical construction.

Electrical attraction by natural products other than amber after they have been rubbed must have been observed by the primitive races of mankind.

Indeed Humboldt in his _Cosmos_ (Lond., 1860, vol. i., p. 182) records a striking instance:

"I observed with astonishment, on the woody banks of the Orinoco, in the sports of the natives, that the excitement of electricity by friction was known to these savage races, who occupy the very lowest place in the scale of humanity. Children may be seen to rub the dry, flat and shining seeds or husks of a trailing plant (probably a _Negretia_) until they are able to attract threads of cotton and pieces of bamboo cane."

[123] PAGE 48, LINE 23. Page 48, line 25. _arsenicum_.--This is _orpiment_.

See the _Dictionary of metallick words_ at the end of Pettus's _Fleta Minor_.

[124] PAGE 48, LINE 23. Page 48, line 26. _in convenienti coelo sicco_.--The observation that only in a dry climate do rock-salt, mica, and rock-alum act as electrics is also of capital importance. Compare page 56.

[125] PAGE 48, LINE 27. Page 48, line 31. _Alliciunt haec omnia non festucas modo & paleas._--Gilbert himself marks the importance of this discovery by the large asterisk in the margin. The logical consequence was his invention of the first _electroscope_, the _versorium non magneticum_, made of any metal, figured on p. 49.

[126] PAGE 48, LINE 34. Page 48, line 36. _quod tantum siccas attrahat paleas, nec folia ocimi._--This silly tale that basil leaves were not attracted by amber arose in the _Quaestiones Convivales_ of Plutarch. It is repeated by Marbodeus and was quoted by Levinus Lemnius as true. Gilbert denounced it as nonsense. Cardan (_De Subtilitate_, Norimb., 1550, p. 132) had already contradicted the fable. "Trahit enim," he says, "omnia levia, paleas, festucas, ramenta {42} tenuia metallorum, & ocimi folia, perperam contradicente Theophrasto." Sir Thomas Browne specifically refuted it. "For if," he says, "the leaves thereof or dried stalks be stripped into small strawes, they arise unto Amber, Wax, and other Electricks, no otherwise then those of Wheat or Rye."

[127] PAGE 48, LINE 34. Page 48, line 38. _Sed vt poteris manifeste experiri...._

Gilbert's experimental discoveries in electricity may be summarized as follows:

1. The generalization of the class of _Electrics_.

2. The observation that damp weather hinders electrification.

3. The generalization that electrified bodies attract everything, including even metals, water, and oil.

4. The invention of the non-magnetic _versorium_ or electroscope.

5. The observation that merely warming amber does not electrify it.

6. The recognition of a definite class of _non-electrics_.

7. The observation that certain electrics do not attract if roasted or burnt.

8. That certain electrics when softened by heat lose their power.

9. That the electric effluvia are stopped by the interposition of a sheet of paper or a piece of linen, or by moist air blown from the mouth.

10. That glowing bodies, such as a live coal, brought near excited amber discharge its power.

11. That the heat of the sun, even when concentrated by a burning mirror, confers no vigour on the amber, but dissipates the effluvia.

12. That sulphur and shell-lac when aflame are not electric.

13. That polish is not essential for an electric.

14. That the electric attracts bodies themselves, not the intervening air.

15. That flame is not attracted.

16. That flame destroys the electrical effluvia.

17. That during south winds and in damp weather, glass and crystal, which collect moisture on their surface, are electrically more interfered with than amber, jet and sulphur, which do not so easily take up moisture on their surfaces.

18. That pure oil does not hinder production of electrification or exercise of attraction.

19. That smoke is electrically attracted, unless too rare.

20. That the attraction by an electric is in a straight line toward it.

[128] PAGE 48, LINE 35. Page 48, line 39. _quae sunt illae materiae._--Gilbert's list of electrics should be compared with those given subsequently by Cabeus (1629), by Sir Thomas Browne (1646), and by Bacon.

The last-named list occurs in his _Physiological Remains_, published posthumously in 1679; it contains nothing new. Sir Thomas Browne's list is given in the following passage, which is interesting as using for the first time in the English language the noun _Electricities_:

"Many stones also both precious and vulgar, although terse and smooth, have not this power attractive; as Emeralds, Pearle, Jaspis, Corneleans, Agathe, Heliotropes, Marble, Alablaster, Touchstone, Flint and Bezoar. Glasse attracts but weakely though cleere, some slick stones and thick glasses indifferently: Arsenic but weakely, so likewise glasse of Antimony, but Crocus Metallorum not at all. Saltes generally but weakely, as Sal Gemma, Alum, and also Talke, nor very discoverably by any frication: but if gently warmed at the fire, and wiped with a dry cloth, they will better discover their Electricities." _(Pseudodoxia Epidemica_, p. 79.)

In the _Philosophical Transactions_, vol. xx., p. 384, is _A Catalogue of Electrical Bodies_ by the late Dr. Rob. Plot. It begins "Non solum succinum," and ends "alumen rupeum," being identical with Gilbert's list except that he calls "Vincentina & Bristolla" by the name "Pseudoadamas Bristoliensis."

[129] PAGE 49, LINE 25. Page 49, line 30. _non dissimili modo._--The _modus_ {43} _operandi_ of the electrical attractions was a subject of much discussion; see Cardan, _op. citat._

[130] PAGE 51, LINE 2. Page 51, line 1. _appellunt._--This appears to be a misprint for _appelluntur_.

[131] PAGE 51, LINE 22. Page 51, line 23. _smyris._--Emery. This substance is mentioned on p. 22 as a magnetic body.

[132] PAGE 52, LINE 1. Page 51, line 46. _gemmae ... vt Crystallus, quae ex limpida concreuit._ See the note to p. 48.

[133] PAGE 52, LINE 30. Page 52, line 32. _ammoniacum._--Ammoniacum, or Gutta Ammoniaca, is described by Dioscorides as being the juice of a ferula grown in Africa, resembling galbanum, and used for incense.

"_Ammoniack_ is a kind of Gum like Frankincense; it grows in Lybia, where _Ammon's_ Temple was." Sir Hugh Plat's _Jewel House of Art and Nature_ (Ed.

1653, p. 223).

[134] PAGE 52, LINE 38. Page 52, line 41. _duae propositae sunt causae ...

materia & forma._--Gilbert had imbibed the schoolmen's ideas as to the relations of matter and form. He had discovered and noted that in the magnetic attractions there was always a verticity, and that in the electrical attractions the rubbed electrical body had no verticity. To account for these differences he drew the inference that since (as he had satisfied himself) the magnetic actions were due to _form_, that is to say to something immaterial--to an "imponderable" as in the subsequent age it was called--the electrical actions must necessarily be due to _matter_. He therefore put forward his idea that a substance to be an electric must necessarily consist of a concreted humour which is partially resolved into an effluvium by attrition. His discoveries that electric actions would not pass through flame, whilst magnetic actions would, and that electric actions could be screened off by interposing the thinnest layer of fabric such as sarcenet, whilst magnetic actions would penetrate thick slabs of every material except iron only, doubtless confirmed him in attributing the electric forces to the presence of these effluvia. See also p. 65. There arose a fashion, which lasted over a century, for ascribing to "humours,"

or "fluids," or "effluvia," physical effects which could not otherwise be accounted for. Boyle's tracts of the years 1673 and 1674 on "effluviums,"

their "determinate nature," their "strange subtilty," and their "great efficacy," are examples.

[135] PAGE 53, LINE 9. Page 53, line 11. _Magnes vero...._--This passage from line 9 to line 24 states very clearly the differences to be observed between the magnetical and the electrical attractions.

[136] PAGE 53, LINE 36. Page 53, line 41. _succino calefacto._--Ed. 1633 reads _succinum_ in error.

[137] PAGE 54, LINE 9. Page 54, line 11. _Plutarchus ... in quaestionibus Platonicis._--The following Latin version of the paragraph in _Quaestio sexta_ is taken from the bilingual edition publisht at Venice in 1552, p.

17 _verso_, liber vii., cap. 7 (or, _Quaestio Septima_ in Ed. Didot, p.

1230).

"Electrum uero quae apposita sunt, nequaquam trahit, quem admodum nec lapis ille, qui sideritis nuncupatur, nec quicqu[=a] a seipso ad ea quae in propinquo sunt, extrinsecus assilit. Verum lapis magnes effluxiones quasdam tum graves, tum etiam spiritales emittit, quibus aer continuatus & iunctus repellitur. Is deinceps alium sibi proximum impellit, qui in orbem circum actus, atque ad inanem locum rediens, ui ferrum fecum rapit & trahit. At Electrum uim quandam flammae similem & spiritalem continet, quam quidem {44} tritu summae partis, quo aperiuntur meatus, foras eijcit. Nam leuissima corpuscula & aridissima quae prope sunt, sua tenuitate atque imbecillitate ad seipsum ducit & rapit, cum non sit adeo ualens, nec tantum habeat ponderis & momenti ad expellendam aeris copiam, ut maiora corpora more Magnetis superare possit & uincere."