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. gemmæ ... vt Crystallus, quæ ex limpidâ 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. duæ propositæ sunt causæ ... 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 quæstionibus Platonicis.—The following Latin version of the paragraph in Quæstio sexta is taken from the bilingual edition publisht at Venice in 1552, p. 17 verso, liber vii., cap. 7 (or, Quæstio Septima in Ed. Didot, p. 1230).