*
A long piece of Iron, even though not excited by a
_loadstone, settles itself toward North and South._
Every good and perfect piece of iron, if drawn out in length, points North
and South, just as the loadstone or iron rubbed with a magnetical body
does; a thing that our famous philosophers have little understood, who have
sweated in vain to set forth the magnetick virtues and the causes of the
friendship of iron for the stone. You may experiment with either large or
small iron works, and either in air or in water. A straight piece of iron
six feet long of the thickness of your finger is suspended (in the way
described in the foregoing chapter) in exact æquipoise by a strong and
slender silken cord. But the cord should be cross-woven of several silk
filaments, not twisted simply in one way; and it should be in a small
chamber with all doors and windows closed, that the wind may not enter, nor
the air of the room be in any way disturbed; for which reason it is not
expedient that the trial should be made on windy days, or while a storm is
brewing. For thus it freely follows its bent, and slowly moves until at
length, as it rests, it points with its ends North and South, just as iron
touched with a loadstone does in shadow-clocks, and in compasses, and in
the mariners' compass. You will be able, if curious enough, to balance all
at the same time by fine threads a number of small rods, or iron wires, or
long pins with which women knit stockings; you will see that all of them at
the same time are in accord, unless there be some error in this delicate
operation: for unless you prepare everything fitly and skilfully, the
labour will be void. Make trial of this thing in water also, which is done
both more certainly and more easily. Let an iron wire two or three digits
long, more or less, be passed through a round cork, so that it may just
float upon water; and as soon as you have committed it to the waves, it
turns upon its own centre, and one end tends to the North, the other to the
South; the causes {31} of which you will afterwards find in the laws of the
direction. This too you should understand, and hold firmly in memory, that
* as a strong loadstone, and iron touched with the same, do not invariably
point exactly to the true pole but to the point of the variation; so does a
weaker loadstone, and so does the iron, which directs itself by its own
forces only, not by those impressed by the stone; and so every ore of iron,
and all bodies naturally endowed with something of the iron nature, and
prepared, turn to the same point of the horizon, according to the place of
the variation in that particular region (if there be any variation
therein), and there abide and rest.
* * * * *