In pursuing his work, Franklin placed a charged jar on a cake of wax and other insulating materials, and drew sparks from it by touching successively the knob and the outer coating, repeating the process a great number of times to his infinite delight. He next attached a brass rod to the outside, bending it and bringing the other end close to the knob (Fig. 16) connected with the inner coating. Between these two he suspended a leaden ball by a silk thread and found, as he expected, that it played to and fro between the terminals for a considerable time. Observe that we have here a definite mass maintained in a state of reciprocating motion by a series of electric attractions and repulsions. We have in fact an electro-motor, closely resembling the star and the chimes of Gordon, the Benedictine, 1745; a mere toy, if you will, but still a remarkable invention. We repeat the same experiment to-day only with a little more harmony, by substituting for the knobs two little bells, which emit a soft, musical note when struck by the interhanging clapper. [Illustration: FIG. 16 Discharge by alternate contacts] This experiment has further significance, for, like Gordon's chimes, it is an instance of the conveyance of electricity from one point of space to another by means of a material carrier, a mode of transfer which has since been called "electric convection," the full meaning of which was not revealed until Rowland (1848-1901), made his famous experiment of 1876 in the laboratory of the University of Berlin with a highly-charged, rapidly-revolving, ebonite disc. It was apropos of this experiment that the illustrious Clerk Maxwell, of the University of Cambridge, wrote to his friend, Professor Tait, of Edinburgh, saying that: "The mounted disc of ebonite Had whirled before, but whirled in vain; Rowland of Troy, that doughty knight, Convection currents did obtain, In such a disc, of power to wheedle From its loved north, the needle." We may here say that Franklin was no stranger to the work done by the electrical pioneers of the Old World, his diligent London friend, Peter Collinson, keeping him advised by means of letters, books and pamphlets, in which inspiration and practical hints must have been found. He certainly was well acquainted with the achievements of Dr. Watson and Dr. Bevis, of London, as well as with the theories and experiments of Dufay and Abbé Nollet in Paris. It is germane to the subject to say that Dr. Bevis used mercury and iron filings for the inner coating of his jars, as well as sheet lead for both. He also experimented with coated panes of glass instead of jars. About this, Franklin wrote to Collinson: "I perceive by the ingenious Mr. Watson's last book, lately received, that Dr. Bevis had used, before we had, panes of glass to give a shock; though till that book came to hand, I thought to have communicated it to you as a novelty." (1748.)