[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_.
[176] PAGE 88, LINE 2. Page 88, line 3. _Coitio verò non fortior._--This heading to chap. xix., taken with the seven lines that follow, and the contrast drawn between _unitio_ and _coitio_, throw much light on the fundamental sense attached by Gilbert to the term _coitio_. It is here clearly used in the sense of _mutual tendency toward union_. Note also the contrasted use in chap. xx. of the verbs _cohære_ and _adhære_. Adhærence connotes a one-sided force (an impossibility in physics), cohærence a mutual force.
[177] PAGE 90, LINE 9. Page 90, line 9. _nempè vt alter polus maius pondus arripiat._--This acute observation is even now not as well known as it ought to be. Only so recently as 1861 Siemens patented the device of fastening a mass of iron to one end of an electromagnet in order to increase the power of the other end. The fact, so far as it relates to permanent magnets was known to Servington Savery. See _Philos. Transactions_, 1729, p. 295.