For very many years electrical experiments followed the lines laid down by Dr. Gilbert; that is, the finding of substances that could be excited or electrified by friction. By and by such substances came to be called electrics, and it became a part of the crude electrical science of the time to compute the force with which these electrics, when excited, attracted or repelled other substances near them. Among the ablest of these investigators were Robert Boyle, author of “Experiments on the Origin of Electricity,” Sir Isaac Newton, Otto von Guericke, and Francis Hawksbee, the last of whom communicated his experiments to the English Royal Society in 1705. Otto von Guericke used a hard roll of sulphur as an electric. He caused it to revolve rapidly while he rubbed or excited it with his hand. Newton and Hawksbee used a revolving glass globe in the same way, and thus became the parents of the modern and better equipped electrical machine used for school purposes.
The next step in electrical discovery, and one which marks an epoch in the history of the science, was made by Stephen Gray, of England, in 1729. To him is due the credit of finding out that electricity from an excited glass cylinder could be conducted away from it to objects at a remote distance. Though he used only a packthread as a conductor, he thus carried electricity to a distance of several hundred feet, and his novel discovery opened up what, for the time, was a brilliant series of experiments in England and throughout France and Germany. Out of these experiments came the knowledge that some substances were natural conductors of electricity, while others were non-conductors; and that the non-conductors were the very substances—glass, resin, sulphur, etc.—which were then in popular use as electrics. Here was laid the foundation of those after-discoveries which led to the selection of copper, iron, and other metals as the natural and therefore best conductors of electricity, and glass, etc., as the best insulators or non-conductors.
Up to this time an excited electric, such as a glass cylinder or wheel, had furnished the only source whence electricity had been drawn for purposes of experiment. But now another great step forward was taken by the momentous discovery that electricity, as furnished by the excited but quickly exhausted electric, could be bottled up, as it were, and so accumulated and preserved in large quantities, to be drawn upon when needed for experiment. It is not known who made this important discovery; but by common consent the storage apparatus, which was to play so conspicuous a part in after-investigations, was named the Leyden Jar or Phial, from the city of Leyden in Holland. It consisted of a simple glass jar lined inside and out with tinfoil to within an inch or two of the top, the tinfoil of the inside being connected by a conductor passing up through the stopper of the jar to a metallic knob on top. This jar could be charged or filled with electricity from a common electric, and it had the power of retaining the charge till the knob on top was touched by the knuckle, or some unelectrified substance, when a spark ensued, and the jar was said to be discharged. By conductors attached to the knob, guns were fired off at a distance by means of the spark, and it is said that Dr. Benjamin Franklin ignited a glass of brandy at the house of a friend by means of a wire attached to a Leyden jar and stretched the full width of the Schuylkill River at Philadelphia.
LEYDEN JAR.
At this stage in the history of eighteenth century electricity there enters a character whose experiments in electricity, and whose writings upon the subject, not only brought him great renown at home and abroad, but perhaps did more to systematize the science and turn it to practical account than those of any contemporary. This was the celebrated Dr. Benjamin Franklin, of Philadelphia, Pa. He showed to the world that electricity was not created by friction upon an electric, but that it was merely gathered there, when friction was applied, from surrounding nature; and in proof of his theory he invaded the clouds with a kite during a thunder-storm, and brought down electricity therefrom by means of the kite-string as a conductor. The key he hung on the string became charged with the electric fluid, and on being touched by an unelectrified body, emitted sparks and produced all the effects commonly witnessed in the discharge of the Leyden jar.
Franklin further established the difference between positive and negative electricity, and showed that the spark phenomenon on the discharge of the Leyden jar was due to the fact that the inside tinfoil was positively electrified and the outside tinfoil negatively. When the inside tinfoil was suddenly drawn upon by a conductor, the spark was simply the result of an effort upon the part of the two kinds of electricity to maintain an equilibrium. By similar reasoning he accounted for the phenomenon of lightning in the clouds, and by easy steps invented the lightning-rod, as a means of breaking the force of the descending bolt, and carrying the dangerous fluid safely to the ground. Here we have not only a practical result growing out of electrical experiments, but we witness the dawn of an era when electricity was to be turned to profitable commercial account. The lightning-rod man has been abroad in the world ever since the days of Franklin.
Thus far, then, electrical science, if science it could yet be called, had gotten on at the dawn of the nineteenth century. No electricity was really known but that produced by friction upon glass, or some other convenient electric. Hence it was called frictional electricity by some, and static electricity by others, because it was regarded as electricity in a state of rest. Though a thing fitted for curious experiment, and a constant invitation to scientific research, it had no use whatever in the arts. An excited electric could furnish but a trivial and temporary supply of electricity. It exhausted itself in the exhibition of a single spark.