aving an axis of iron: this axis rested on
stone blocks, and threw off from time to time great quantities of rust,
which, mixing with the particles of stone and the oil used to facilitate
the motion, became conglomerated into a hardened mass: this mass had all
the properties of the native magnet. The bell is supposed to have been in
the same position for 400 years."

[214] PAGE 142, LINE 13. Page 142, line 15. _tunc planetae & corpora
coelestia._--Gilbert's extraordinary detachment from all metaphysical and
ultra-physical explanations of physical facts, and his continual appeal to
the test of experimental evidence, enabled him to lift the science of the
magnet out of the slough of the dark ages. This passage, however, reveals
that he still gave credence to the _nativities_ of judicial Astrology, and
to the supposed influence of the planets on human destiny.

[215] PAGE 144, LINE 14. Page 144, line 14. _ijdem._--The editions of 1628
and 1633 erroneously read _iisdem_.

[216] PAGE 147, LINE 27. Page 147, line 29. _ex optimo aciario._--Gilbert
recommended that the compass-needle should be of the best steel. Though the
distinction between iron and steel was not at this time well established,
there is no reason to doubt that by _aciarium_ was meant edge-steel as used
for blades. Barlowe, in his _Magneticall Advertisements_ (Lond., 1616), p.
66, gives minute instructions for the fashioning of the compass-needle. He
gives the preference to a pointed oval form, and describes how the steel
must be hardened by heating to whiteness and quenching in water, so that it
is "brickle in a manner as glass it selfe," and then be tempered by
reheating it over a bar of red hot iron until it is let down to a blue
tint. Savery (_Philos. Trans._, 1729) appears to have been the first to
make a systematic examination of the magnetic differences between hard
steel and soft iron.

Instructions for touching the needle are given in the _Arte de Nauegar_ of
Pedro de Medina (Valladolid, 1545, lib. vi., cap. 1).

[217] PAGE 149, LINE 8. Page 149, line 9. _per multa saecula._--Compare
Porta's assertion (p. 208, English edition) "iron once rubbed will hold the
vertue a hundred years." Clearly not a matter within the actual experience
of either Porta or Gilbert.

[218] PAGE 153, LINE 2. Page 153, line 2. _Cardani ab ortu stellae in cauda
vrsae._--What Cardan said (_De Subtilitate_, _Edit. citat._, p. 187) was:
"ortum stellae in cauda ursae minoris, q