[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 æstus ratione aliàs._--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, quàm humorem & spiritum subterraneum; nec plus resistit interposita terra, quàm 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.