« ZurückWeiter »
This was approved of, and signed by twelve hundrcal persons immediately Copies were instantly circulated throughout the province; and, in a short time, the number of signers amounted to ten thousand. Franklin was chosen colonel of the Philadelphia regiment; but he did not think proper to accept of the honour.
Pursuits of a different nature now occupied the greatest part of his attention for some years. He en. gaged in a course of electrical experiments, with all the ardour and thirst for discovery wnich character
of experimental philosophy, electricity had been least explored. The attractive power of amber is incritioned by Theophrastus and Pliny, and from them, by later naturalists. In the year 1600, Gilbert, an Eng. lish physician, enlarged, considerably, the catalogue of substances which have the property of attracting lignt bodies. Boyle, Otto Guericke, a burgomaster of Magdeburg, celebrated as the inventor of the airpump, Dr. Wall, and Sir Isaac Newton, added some facts. Guericke first observed the repulsive power of electricity, and the light and noise produced by it. In 1709, Hawkesbec communicated some important observations and experiments to the world. For se
Mr. Grey applied himself to it, in 1728, with great assiduity. He and his friend, M:.Wheeler, made a great
that electricits may be communicated from one body to another, even without being in contact, and in this way may be conducted to a great distance. Mr. Grey afterwards folind, that, by suspending rods of iron oy silk or hair lines, and bringing an excited tube under them, sparks might be drawn, and a light perceived at the extremities in the dark. M. Du Faye, intendant of the French king's gardens, made a number of experiments, which added not a little to the science. He made the discovery of two kinds of electricity, which he called vitreous and resinous; the forner produced by rubbing glass, the latter from excited sulphur, sealing-wax, &c. But this idea he afterwards gave up as erroneous. Between the years 1739 and 1742, Desauguliers made a number of experiments, but added little of importance. He first used the terms conductors and electrics per se. In 1742, several ingenious Germans engaged in this subject; of these the principal were, professor Boze, of Wittemberg, professor Winkler, of Leipsic, Gordon, a Scotch Benedictine monk, professor of philosophy at Erfurt, and Dr. Ludolf, of Berlin. The result of their researches astonished the philosophers of Europe. Their apparatus was large, and by means of it they were enabled to collect large quantities of the electric tluid, and thus to produce phenomena which had been hitherto unobserved. They killed small birds, and set spirits on fire. Their experiments excited the curiosity of other philosophers. Collinson, about the year 1745, sent to the Library Company of Philadel. phia, an account of these experiments, together with à tube, and directions how to use it. Franklin, with some of his friends, immediately engaged in a course of experiments, the result of which is well known). He was enabled to make a number of important discoveries, and to propose theories to account for various phenomena, which have been universally adopted, and which bid fair to endure for ages. His observations he communicated, in a series of letters, to his friend Collinson; the first of which is dated March 28, 1747. In these he shows the power of points in drawing and throwing off the electrical inatter, which had hitherto escaped the notice of electricians. He also made the grand discovery of a plus and minus, or of a positive and negative state of electricity. We give him the honour of this, without hesitation; although the English hava claimed it for their countryman, Dr. Watson. Watson's paper is dated January 21, 1748 ; Franklin's, July 11, 1747; several monilis prior. Shortly after, Franklin, from his principles of the plus and minus stats, explained, in a satisfactory manner, the phenomena of the Leyden phial, first observed by Mr. Cuneus, or by professor Muschenbroeck, of Leyden, which had much perplexed philosophers. He showed clearly, that the bottle, when charged, contained no more electricity than before, but that as much was taken from ono side as was thrown on the other; and that, to dis. charge it, nothing was necessary but to produce a communication between the two sides by which the equilibrium might be restored, and that then no signs of electricity would remain. He afterwards dernonstrated, by experiments, that the electricity did not reside in the coating, as had been supposed, but in the pores of the glass itself. After a phial was charged, he removed the coating, and found that upon applying a new coating, the shock might still be received. In the year 1749, he first suggested his idea of explaining the phenomena of thundergusts, and of the auroraborealis, upon electrical principles. He points out many particulars in which lightning and electricity agree ; and he adduces many facts, and reasonings from facts, in support of his positions. In the same year he conceived the astonishingly bold and grand idea of ascertaining the truth of his doctrine, by ac. tually drawing down the lightning, by means of sharp pointed iron rods raised into the region of the clouds. Even in this uncertain state, his passion to be useful to mankind displays itself in a powerful manner. Admitting the identity of electricity and lightning, and knowing the power of points in repelling bodies charged with electricity, and in conducting their fires silently and imperceptibly, he suggested the idea of securing houses, ships, &c. from being damaged by lightning, by erecting pointed rods, that should rise some feet above the most elevated part, and descend some feet into the ground or the water. The effect of these, he concluded, would be either to prevent a stroke, by repelling the cloud beyond the striking distance, or by drawing off the electrical fire which it contained; or, if they could not effect this, they would at least conduct the electric matter to the earth, without any ir. jury to the building.
It was not until the summer of 1752, that he was enabled to complete his grand and unparalleled discovery by experiment. The plan which he had originally proposed, was to erect on some high tower, oi other elevated place, a sentry-box, from which should rise a pointed iron rod, insulated by being fised in a cake of resin. Electrified clouds passing over this,
would, he conceived, impart to it a portion of their electricity, which would be rendered evident to the senses by sparks being emitted, when a key, the knuckle, or other conductor, was presented to it. Philadelphia at this time afforded no opportunity of trying an experiment of this kind. While Franklin was waiting for the erection of a spire, it occurred to him that he might have more ready access to the region of clouds by meais of a common kite. He prepared one by fastening two cross sticks to a silk handkerchief, which would not suffer so much from the rain as paper. To the upright stick was affixed an iron point. The string was, as usual, of hemp, except the lower end, which was silk. Where the hempen string terminated, a key was fastened. With this apparatus, on the appear. ance of a thundergust approaching, he went out into the commons, accompanied by his son, to whom alone he communicated his intentions, well knowing the ridicule which, too generally for the interest of science, awaits unsuccessful experiments in philosophy. He placed himsei: under a shade, to avoid the rain-his kite was raised-a thunder-cloud passed over it-no sign of electricity appeared. He almost despaired of success, when, suddenly, he observed the loose fibres of his string to move towards an erect position. He now presented his knuckle to the key, and received a strong spark. How exquisite must his sensations have been at this moment ! On this experiment depended the fate of his theory. If he succeeded, his name would rank high among those who had improved science; if he failed, he must inevitably be subjected to the derision of mankini, or, what is worse, their pity, as a well-meaning man, but a weak, silly projector The anxiety with which he looked for the result of his experiment, may be easily conceived. Doubts and despair had begun to prevail, when the fact wus ascertained in so clear a manner, that even the most incredulous could no longer withhold their assent. Repeated sparks were drawn from the key, a phial was charged, a shock given, and all the experiments made which are usually performed with electricity.
About a month before this period, some ingenious Frenchman had completed the discovery in the man
ner originally proposed by Dr. Franklin. The letters which he sent to Mr. Collinson, it is said, were refused a place in the Transactions of the Royal Society of London. However this may be, Collinson published them in a separate volume, under the title of “ New Experiments and Observations on Electricity, made at Philadelphia, in America.” They were read with avidity, and soon translated into different languages. A very incorrect French translation féll into the hands of the celebrated Buffon, who, notwithstanding the disadvantages under which the work laboured, was much pleased with it, and repeated the experiments with success. He prevailed on his friend, M. D'Alibard, to give his countrymen a more correct translation of the works of the American electrician. This contributed much towards spreading a knowledge of Franklin's principles in France. The king, Louis XV. hearing of these experiments, expressed a wish to be a spectator of them. A course of experiments was given at the seat of the Duc D'Ayen, at St. Gerinain, by M. de Lor. The applauses vhich the King bestowed upon Franklin, excited in Buffon, D'Alibard, and De Lor, an earnest desire of ascertaining the truth of his theory of thundergust. Buffon erected his apparatus on the tower of Montbar, M. D'Alibard at Mary-la-ville, and De Lor at his house in the Estrapade at Paris, some of the highest ground in that capi. tal. D'Alibard's machine first showed signs of electricity. On the 10th of May, 1752, a thunder-cloud passed over it, in the absence of M. D'Alibard, and a number of sparks were drawn from it by Coiffier, a joiner, with whom D'Alibard had left directions how to proceed, and by M. Raulet, the prior of Mary-laville. An account of this experiment was given to the Royal Acadery of Sciences, by M. D’Alibard, in a Memoir, dated May 13th, 1752. On the 18th of May, M. de Lor proved equally successful with the appara, tus erected at his own house. These philosophers soon excited those of other parts of Europe to repeat the experiment, among whom, none signalized themselves inore than Father Beccaria, of Turin, to whose observations science is much indebted. Even the cold regions of Russia were penetrated by the ardour for