Imágenes de páginas

restored, and that then no signs of electricity would remain. He afterwards demonstrated 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 thunder-gusts, and of the aurora borealis, upon electrical principles. He points out many particulars in which lightning and electricity agree; and he adduces many facts, and reasoning 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 actually drawing down the forked 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 fire silently and imperceptibly, he suggests the idea of securing houses, ships, &c. from being damaged by lightning, by erecting pointed iron rods, which 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 stroke to the earth, without any injury 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, or other elevated place, a sentery-box, from which should rise a pointed iron rod, insulated by being fixed in a cake of resin. Electrified clouds passing over this would, he conceived, impart to it a portion of their eléctricity, which would be rendered evident to the senses by sparks being emitted, when a key, a knuckle, or other conductor was presented to it. Philadelphia at this time afforded no opportunity of trying an experiment of this kind. Whilst 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 means of a common kite. He prepared one by attaching two cross sticks to a silk handkerchief, which would not suffer so much from the rain as paper. To his 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 appearance of a thunder-gust 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 himself under a shed to avoid the rain. His kite was raised. A thundercloud 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 amongst those who have improved science; if he failed, he must inevitably be subjected to the derision of mankind, 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 easily be conceived. Doubts and despair had begun to prevail, when the fact was 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 Leyden 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 Frenchmen had completed the discovery in the manner originally proposed by Dr. Franklin. The letters which he sent to Mr. Collinson, it is said, were refused a place amongst the papers 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 fell into the hands of the celebrated Buffon, who, notwithstanding the disadvantages under which the work labored, was much pleased with it, and repeated the experiments with success. He prevailed upon his friend, M. D'Alibard, to give to his countrymen a more correct translation of the work 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. Germains, by M. De Lor. The applauses which the king bestowed upon Franklin, excited in Buffon, D’Alibard, and De Lor, an earnest desire of ascertaining the truth of his theory of thunder-gusts. Buffon erected his apparatus on the tower of Montbar, M. D’Alibard at Marly-la-ville, and De Lor at his house in the Estrapade at Paris, some of the highest ground in that capital. D’Alibard's machine first showed signs of electricity. On the 10th of May, 1752, a thunder-cloud passed over it, in the VOL. I,


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 Marly-la-ville. An account of this experiment was given to the Royal Academy of Sciences, in a memoir by M.D'Alibard, dated May 13, 1752. On the 18th of May, M. De Lör proved equally successful with the apparatus erected at his own house. These discoveries soon excited the philosophers of other parts of Europe to repeat the experiment. Amongst these, none signalised themselves more than Father Beccaria of Turin, to whose observations science is much indebted. Even the cold regions of Russia were penetrated by the ardor for discovery. Professor Richman bade fair to add much to the stock of knowledge on this subject, when an unfortunate flash from his rod put a period to his existence. The friends of science will long remember with regret the amiable martyr to electricity.

“ By these experiments Franklin's theory was established in the most firm manner. When the truth of it could no longer be doubted, the vanity of men endeavored to detract from its merit. That an American, an inhabitant of the obscure city of Philadelphia, the name of which was hardly known, should be able to make discoveries, and to frame theories, which had escaped the notice of the enlightened philosophers of Europe, was too mortifying to be admitted. He must certainly have taken

« AnteriorContinuar »