« SebelumnyaLanjutkan »
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 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 actually drawing down the lightning with sharppointed 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 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 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 sentry-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 electricity, which would be rendered eyident 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 means 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 appearance of a thunder-gust approaching, he went out into the common, accompanied by his son, to whom alone he communicated his intentions, well knowing the ridicule which, too generally for the interests of science, awaits unsuccessful experiments in philosophy. He placed himself 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 mankind, or, what is worse, their pity, as a wellmeaning 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 was ascertained in so clear a manner, that even the most incredulous çould 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 manner originally proposed by Dr Franklin. The letters
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 fell 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 countryman 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. 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-gust. Buffon erected his apparatus on the tower of Montbar, M. D'Alibard at Mary-la-ville, and De Lor at his house in the Estrapede 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 absence of M. D’Alibard, and a number of sparks were drawn from it by Coffier, a joiner, with whom D’Alibard had left directions how to proceed, and by M. Raulet, the prior of Mary-la-ville. An account of this experiment was given to the Royal Academy 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 apparatus erected at his own house. These philosophers soon excited those of other parts of Europe to repeat the experiment; amongst whom none signalized themselves more than father Beccaria
of Turin, to whose observations science is much indebted. Even the cold regions of Russia were penetrated by the ardour for discovery. Professor Richman bade fair to add much to the stock of knowledge on this subject, when an unfortunate flash from his conductor 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 convincing manner. When the truth of it could no longer be doubted, envy and vanity endeavoured 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 the idea from some one else. An American, a being of an inferior order, make discoveries Impossible! It was said, that the abbé Nollet, in 1748, had suggested the idea of the similarity of lightning and electricity in his Leçons de Phisique. It is true, that the abbé mentions the idea, but he throws it out as a bare conjecture, and proposes no mode of ascertaining the truth of it. He himself acknowledges, that Franklin first entertained the bold thought of bringing lightning from the heavens, by means of pointed rods fixed in the air. The similarity of lightning and electricity is so strong, that we need not be surprised at notice being taken of it, as soon as electrical phenomena become familiar. We find it mentioned by Dr Wall and Mr Grey, while the science was in its infancy. But the honour of forming a regular theory of thunder-gusts, of suggesting ă mode of determining the truth of it by experiments, and of putting these experiments in practice, and thus establishing the theory upon a firm and solid basis, is incontestibly due to Franklin. D’Alibard, who made the first
experiments in France, says that he only followed the track which Franklin had pointed out.
“ It has been of late asserted, that the honour of completing the experiment with the kite does not belong to Franklin. Some recent English paragraphs have attributed it to some Frenchman, whose name they do not mention; and the abbé Bertholon gives it to M. de Romas, assessor to the presideal of Nerac: the English paragraphs probably refer to the same person. But a very slight attention will convince us of the injustice of this procedure : Dr Franklin's experiment was made in June 1752; and his letter, giving an account of it, is dated October 19, 1752. M. de Romas made his first attempt on the 14th of May 1753, but was not successful until the 7th of June ; a year after Franklin had completed the discovery, and when it was known to all the philosophers in Europe.
6 Besides these great principles, Franklin's letters on electricity contain a number of facts and hints, which have contributed greatly towards reducing this branch of knowledge to a science. His friend, Mr Kinnersley, communicated to him a discovery of the different kinds of electricity excited by rubbing glass and sulphur. This was first observed by M. du Faye; but it was for many years neglected. The philosophers were disposed to account for the phenomena rather from a difference in the quantity of electricity collected ; and even Du Faye himself seems at last to have adopted this doctrine. Franklin at first entertained the same idea; but, upon repeating the experiments, he perceived that Mr. Kinnersley was right, and that the vitreous and resinous electricity of Du Faye were nothing more than the positive and negative states which he had before observed ; and that the glass globe charged positively, or increased the quantity of electricity on the prime conductor, while the globe of sulphur diminished its natural quantity, or charged negatively. These experiments