equal to the obtuse and equilateral angle of this Crystal. I say,
further, that if these corpuscles were lightly stuck together, on
breaking this pyramid it would break along faces parallel to those
that make its point: and by this means, as it is easy to see, it would
produce prisms similar to those of the same crystal as this other
figure represents. The reason is that when broken in this fashion a
whole layer separates easily from its neighbouring layer since each
spheroid has to be detached only from the three spheroids of the next
layer; of which three there is but one which touches it on its
flattened surface, and the other two at the edges. And the reason why
the surfaces separate sharp and polished is that if any spheroid of
the neighbouring surface would come out by attaching itself to the
surface which is being separated, it would be needful for it to detach
itself from six other spheroids which hold it locked, and four of
which press it by these flattened surfaces. Since then not only the
angles of our crystal but also the manner in which it splits agree
precisely with what is observed in the assemblage composed of such
spheroids, there is great reason to believe that the particles are
shaped and ranged in the same way.
[Illustration: {Pyramid and section of spheroids}]
There is even probability enough that the prisms of this crystal are
produced by the breaking up of pyramids, since Mr. Bartholinus relates
that he occasionally found some pieces of triangularly pyramidal
figure. But when a mass is composed interiorly only of these little
spheroids thus piled up, whatever form it may have exteriorly, it is
certain, by the same reasoning which I have just explained, that if
broken it would produce similar prisms. It remains to be seen whether
there are other reasons which confirm our conjecture, and whether
there are none which are repugnant to it.
[Illustration: {paralleloid arrangement of spheroids with planes of
potential cleavage}]
It may be objected that this crystal, being so composed, might be
capable of cleavage in yet two more fashions; one of which would be
along planes parallel to the base of the pyramid, that is to say to
the triangle ABC; the other would be parallel to a plane the trace of
which is marked by the lines GH, HK, KL. To which I say that both the
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