about a tenth of an inch in thickness and there are ten of them in
number. To what known cause can this exactly regular distribution of so
many earthy strata of different colours surrounding the nucleus be
ascribed? I don't know that any mineralogists have attempted an
explanation of this wonderful phenomenon. I suspect it is owing to the
polarity of the central nucleus. If iron-filings be regularly laid on
paper by means of a small sieve, and a magnet be placed underneath, the
filings will dispose themselves in concentric curves with vacant
intervals between them. Now if these iron-filings are conceived to be
suspended in a fluid, whose specific gravity is similar to their own,
and a magnetic bar was introduced as an axis into this fluid, it is easy
to foresee that the iron filings would dispose themselves into
concentric spheres, with intervals of the circumnatant fluid between
them, exactly as is seen in these nodules of iron-earth. As all the
lavas consist of one fourth of iron, (Kirvan's Mineral) and almost all
other known bodies, whether of animal or vegetable origin, possess more
or less of this property, may not the distribution of a great portion of
the globe of the earth into strata of greater or less regularity be
owing to the polarity of the whole?]

[_And turn to adamant_. l. 192. The circumstances which render iron more
valuable to mankind than any other metal are, 1. its property of being
rendered hard to so great a degree and thus constituting such excellent
tools. It was the discovery of this property of iron, Mr. Locke thinks,
that gave such pre-eminence to the European world over the American one.
2. Its power of being welded; that is, when two pieces are made very hot
and applied together by hammering, they unite compleatly, unless any
scale of iron intervenes; and to prevent this it is usual for smiths to
dip the very hot bar in sand, a little of which fuses into fluid glass
with the scale and is squeezed out from between the uniting parts by the