with the very gentlest rubbing, often even
without rubbing; they also excite more strongly, and retain hold for a
longer time, because they have stronger effluvia and last longer. But
diamond, glass, rock-crystal, * and numerous others of the harder and
firmly concreted gems first grow warm: therefore at first they are rubbed
longer, and then they also attract strongly; nor are they otherwise set
free into vapour. Everything rushes towards electricks[143] excepting
flame, and flaming bodies, and the thinnest air. Just as they do not draw
flame, in like manner they do not affect a versorium, if on any side it is
very near to a flame, either the flame of a lamp or of any burning matter.
It is manifest indeed that the effluvia are destroyed by flame and igneous
* heat; and therefore they attract neither flame nor bodies very near a
flame. For electrical effluvia have the virtue of, and are analogous with,
extenuated humour; but they will produce their effect, union and
continuity, not by the external impulse of vapours, not by heat and
attenuation of heated bodies, but by their humidity itself attenuated into
its own peculiar effluvia. Yet they entice * smoke sent out by an
extinguished light; and the more that smoke is attenuated in seeking the
upper regions, the less strongly is it turned aside; for things that are
too rarefied are not drawn to them; and at length, when it has now almost
vanished, it does not * incline towards them at all, which is easily seen
against the light. When in fact the smoke has passed into air, it is not
moved, as has been demonstrated before. For air itself, if somewhat thin,
is not attracted in any way, unless on account of succeeding that which has
vacated its place, as in furnaces and such-like, where the air is fed in by
mechanical devices for drawing it in. Therefore an effluvium resulting from
a non-fouling friction, and one which {60} is not changed by heat, but
which is its own, causes union and coherency, a prehension and a congruence
towards its source, if only the body to be attracted is not unfitted for
motion, either by the surroundings of the bodies or by its own weight. To
the bodies therefore of the electricks themselves small bodies are borne.
The effluvia extend out their virtue--effluvia which are proper and
peculiar to them, and _sui generis_, differing from common air, being
produced from humour, excited by a calorifick motion from attrition and
attenuation. And as if they w