is removed.
The plate is then placed in a solar microscope, and an image of the
film is thrown upon a white screen. The warmth of the illuminating
beam adds itself to that already imparted to the glass plate, so that
after a moment or two the dissolved salt can no longer exist in the
liquid condition. Molecule then closes with molecule, and you have a
most impressive display of crystallizing energy overspreading the
whole screen. You may produce something similar if you breathe upon
the frost ferns which overspread your window-panes in winter, and then
observe through a pocket lens the subsequent recongelation of the
film.

In this case the crystallizing force is hampered by the adhesion of
the film to the glass; nevertheless, the play of power is strikingly
beautiful. Sometimes the crystals start from the edge of the film and
run through it from that edge; for, the crystallization being once
started, the molecules throw themselves by preference on the crystals
already formed. Sometimes the crystals start from definite nuclei in
the centre of the film, every small crystalline particle which rests
in the film furnishing a starting-point. Throughout the process you
notice one feature which is perfectly unalterable, and that is,
angular magnitude. The spiculae branch from the trunk, and from these
branches others shoot; but the angles enclosed by the spiculae are
unalterable. In like manner you may find alum-crystals,
quartz-crystals, and all other crystals, distorted in shape. They are
thus far at the mercy of the accidents of crystallization; but in one
particular they assert their superiority over all such
accidents--_angular magnitude_ is always rigidly preserved.

My second example of the action of crystallizing force is this: By
sending a voltaic current through a liquid, you know that we decompose
the liquid, and if it contains a metal, we liberate this metal by
electrolysis. This small cell contains a solution of acetate of lead,
which is chosen for our present purpose, because lead lends itself
freely to this crystallizing power. Into the cell are dipped two very
thin platinum wires, and these are connected by other wires with a
small voltaic battery. On sending the voltaic current through the
solution, the lead will be slowly severed from the atoms with which it
is now combined; it will be liberated upon one of the wires, and at
the moment of its liberation it will obey the polar forces of its
atoms, and prod