He also noted that an equilibrium could not be restored in the bottle by inward communication or contact of the parts, but only by a communication, formed without the bottle between its top and bottom. He also noted that no electrical fire could be thrown into the top of the bottle, when none could get out at its bottom, either because the bottom was too thick, or because it stood on some non-conducting material, and likewise that, when the bottle was electrified, but little of the electrical fire could be drawn from the top by touching the wire, unless an equal quantity could at the same time get in at the bottom. So wonderfully [he adds] are these two states of electricity, the _plus_ and _minus_, combined and balanced in this miraculous bottle! situated and related to each in a manner that I can by no means comprehend! If it were possible that a bottle should in one part contain a quantity of air strongly comprest, and in another part a perfect vacuum, we know the equilibrium would be instantly restored _within_. But here we have a bottle containing at the same time a _plenum_ of electrical fire, and a _vacuum_ of the same fire; and yet the equilibrium cannot be restored between them but by a communication without! though the _plenum_ presses violently to expand, and the hungry vacuum seems to attract as violently in order to be filled. The letter concludes with an elaborate statement of the experiments by which the correctness of its conclusions could be established. Franklin's next discovery communicated to Collinson in a letter dated the succeeding year was that, when the bottle was electrified, the electric fluid resided in the glass itself of the bottle. The manner in which he proved this fact is a good example of his inductive thoroughness.