_Excite the glass tube, and approach the prime conductor with
it, holding it across, near the end opposite to that on which
the threads hang, at the distance of five or six inches. Keep it
there a few seconds, and the threads of the tassels will diverge.
Withdraw it, and they will close._
They diverge, because they have received electric atmospheres
from the electric matter before contained in the substance of the
prime conductor; but which is now repelled and driven away, by the
atmosphere of the glass tube, from the parts of the prime conductor
opposite and nearest to that atmosphere, and forced out upon the
surface of the prime conductor at its other end, and upon the threads
hanging thereto. Were it any part of the atmosphere of the glass
tube that flowed over and along the prime conductor to the threads,
and gave them atmospheres (as is the case when a spark is given to
the prime conductor from the glass tube) such part of the tube's
atmosphere would have remained, and the threads continue to diverge;
but they close on withdrawing the tube, because the tube takes with
it _all its own atmosphere_, and the electric matter, which had
been driven out of the substance of the prime conductor, and formed
atmospheres round the threads, is thereby permitted to return to its
place.
_Take a spark from the prime conductor near the threads, when they
are diverged as before, and they will close._
For by so doing you take away their atmospheres, composed of the
electric matter driven out of the substance of the prime conductor,
as aforesaid, by the repellency of the atmosphere of the glass tube.
By taking this spark you rob the prime conductor of part of its
natural quantity of the electric matter; which part so taken is not
supplied by the glass tube, for when that is afterwards withdrawn, it
takes with it its whole atmosphere, and leaves the prime conductor
electrised negatively, as appears by the next operation.
_Then withdraw the tube, and they will open again._
For now the electric matter in the prime conductor, returning to its
equilibrium, or equal diffusion, in all parts of its substance, and
the prime conductor having lost some of its natural quantity, the
threads connected with it lose part of theirs, and so are electrised
negatively, and therefore repel each other, by _Pr. III._
_Approach the prime conductor with the tube near the same place as
at first, and they will close again._
Because the part of their natural quantity of electric fluid, which
they had lost, is now restored to them again, by the repulsion of the
glass tube forcing that fluid to them from other parts of the prime
conductor; so they are now again in their natural state.
_Withdraw it, and they will open again._
For what had been restored to them, is now taken from them again,
flowing back into the prime conductor, and leaving them once more
electrised negatively.
_Bring the excited tube under the threads, and they will diverge
more._
Because more of their natural quantity is driven from them into the
prime conductor, and thereby their negative electricity increased.