It was not until the year 1600 that Dr. William Gilbert, physician to Queen Elizabeth, made a great step forward by showing in his celebrated work, ‘De magnete, magneticisque corporibus, et de magno magnete tellure, physiologia nova,’ that the two classes of phenomena, the magnetic and the electric, are emanations of a single fundamental force pervading all nature. Dr. Gilbert further discovered that many other substances besides amber possess the electric power, and that this power is easily excited when the air is dry and cool, and with difficulty when it is moist and warm. These discoveries caused great commotion in the European learned world, yet produced no further result for another half a century. In 1650, Otto von Guericke, burgomaster of Magdeburg, the inventor of the air-pump, who had studied with deep interest Dr. Gilbert’s book, succeeded in constructing a little electrical machine, composed mainly of a ball of sulphur mounted on a revolving axis. By the aid of this instrument, very rude in construction, he produced powerful sparks and flashes of electric light, and it helped him likewise to discover, first, that bodies excited by friction communicate their electricity to other bodies by mere contact, and, secondly, that there resides in electrified substances the power of repulsion as well as that of attraction. Those who followed in the wake of the ingenious burgomaster of Magdeburg for the next ninety or hundred years, till towards the middle of the eighteenth century, did very little towards adding to the already acquired knowledge of electricity. Sir Isaac Newton constructed an electrical machine of glass, very superior to that of Otto von Guericke, with which he made some amusing experiments; but, strangely enough, drew no conclusions from them, treating the mighty force under his eyes as only a plaything. This was all the more singular as a contemporary of the great philosopher, Francis Hauksbee, like him a Fellow of the Royal Society, called attention, in a volume entitled ‘Physico-mechanical Experiments,’ published in 1709, to the great similarity between the electric flash and lightning, hinting that the two might possibly be offspring of the same mysterious force. Dr. Wall, in 1708, said that the light and crackling of rubbed amber seemed in some degree to represent thunder and lightning. Another member of the Royal Society, Stephen Gray--the first man in England who made the study of electricity the devotion of his life, but of whose career very little is known beyond the fact that he was very poor, and a pensioner of the Charterhouse--added numberless experiments to those previously made, and was bold enough to declare, in 1720, six years before Sir Isaac Newton’s death, that ‘electricity seems to be of the same nature with thunder and lightning--if we may compare great things with small.’ For this audacity in ‘comparing things’ he was sharply taken to task by