eminent electricians down the ages. Fig. 11 shows the modern form of the jar with movable coatings. [Illustration: FIG. 12 Three coated panes in _series_] [Illustration: FIG. 13 Three panes in _parallel_] In the "fulminating" pane, as it came to be called, we have one of the eleven elements of Franklin's historic battery of 1748. It is interesting to notice that he was accustomed to connect his "panes" in series while charging (Fig. 12), but that he preferred to join similar coatings together, that is, to couple them in "parallel" (Fig. 13), for powerful discharges. Fig. 14 shows three jars in "parallel." Later on, he arranged Leyden jars so that the inside coating of one could be hooked to the outside coating of another, the first of the series hanging down from the prime conductor of the machine, while the last one was grounded. "What is driven out of the tail of the first," he quaintly says, "serves to charge the second; what is driven out of the second serves to charge the third, and so on." This has become known as the "cascade" method of charging a battery, owing to the flow of electricity from one jar to the next (Fig. 15). Electricians, however, have discarded the picturesque "cascade" for the prosaic term of "series" or "tandem" arrangement. [Illustration: FIG. 14 Three jars in _parallel_] [Illustration: FIG. 15 Three jars in _cascade_] Franklin also noticed that a phial cannot be charged while standing on wax or on glass, or even while hanging from the prime conductor, unless communication be formed between its outer coating and the floor, the reason given being that "the jar will not suffer a charging unless as much fire can go out of it one way as is thrown in by the other." (1748.) Following his very ingenious Philadelphia friend and co-worker, Kinnersley, he varies the mode of charging by electrifying the outside of the jar and grounding the inner coating; for "the phial will be electrified as strongly if held by the hook and the coating applied to the globe as when held by the coating and the hook applied to the globe." (1748.) The globe here referred to is the glass globe of Franklin's frictional machine of American make, which, when rotated, was electrified positively by contact with the hand or with a leather rubber. Franklin also used a sulphur ball or "brimstone" globe, and observed that the electrification produced on it differed in kind from that developed on the glass globe. (1752.) It may here be stated that the first to use a _leather cushion_ as a substitute for the hand in the frictional machine, was Winkler, of Leipzig (1745); the efficiency of the rubber was increased by Canton, of London, who covered it with an _amalgam_ of tin and mercury (1762). Bose, of Wittenberg, had previously added the _prime-conductor_, which greatly augmented the electrical capacity and output of the machine.