Otto von Guericke, Burgomaster of Magdeburg, contemporary of Boyle, and inventor of the air-pump, intensified the electric power previously obtained. He devised what may be called the first electrical machine, which was a ball of sulphur, about the size of a child's head. Turned by a handle and rubbed by the dry hand, the sulphur-sphere emitted light in the dark.
Von Guericke also noticed that a feather, having been first attracted toward his sulphur globe, was afterward repelled, and kept at a distance from it, until, having touched another body, it was again attracted. He also heard the hissing of the "electric fire," and observed that a body, when brought near his excited sphere, became electrical and capable of being attracted.
The members of the Academy del Cimento examined various substances electrically. They proved smoke to be attracted, but not flame, which, they found, deprived an electrified body of its power.
They also proved liquids to be sensible to the electric attraction, showing that when rubbed amber was held over the surface of a liquid, a little eminence was formed, from which the liquid was finally discharged against the amber.
Sir Isaac Newton, by rubbing a flat glass, caused light bodies to jump between it and a table. He also noticed the influence of the rubber in electric excitation. His gown, for example, was found to be much more effective than a napkin. Newton imagined that the excited body emitted an elastic fluid which penetrated glass.
Dr. Wall (1708) experimented with large, elongated pieces of amber. He found wool to be the best rubber of amber. "A prodigious number of little cracklings" was produced by the friction, every one of them being accompanied by a flash of light. "This light and crackling," says Dr. Wall, "seem in some degree to represent thunder and lightning."[1] This is the first published allusion to thunder and lightning in connection with electricity.
Stephen Gray (1729) also observed the electric brush, snappings, and sparks. He made the prophetic remark, that "though these effects are at present only minute, it is probable that in time there may be found out a way to collect a greater quantity of the electric fire, and, consequently, to increase the force of that power which by several of those experiments, if we are permitted to compare great things with small, seems to be of the same nature with that of thunder and lightning."[2]
Sec. 3. The Art of Experiment.—We have thus broken ground with a few historic notes, intended to show the gradual growth of electrical science. Our next step must be to get some knowledge of the facts referred to, and to learn how they may be produced and extended. The art of producing and extending such facts, and of inquiring into them by proper instruments, is the art of experiment.
