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[3] The camera obscura (dark chamber) is a closed space impervious to light. Porta, the inventor here referred to, was a Neapolitan physician. He found that by fixing a double convex lens in the aperture, and placing a white screen in the focus, the image was much brighter and more definite.
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[4] Galvani was a professor of anatomy in the university of Bologna. While engaged in his anatomical investigations he observed, accidently so to say, that when the lumbar nerves of a dead frog were connected with the crural muscles by a metallic circuit, the latter became briskly contracted. The electricity theory drawn by Galvani from his observation of the frog was chiefly opposed by the philosopher likewise here mentioned, Alexander Volta, professor of physics in Pavia.
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[5] Oerstedt’s discovery, published in the year 1819, was afterwards considerably extended by Ampère and Faraday. It laid, however, the foundation of the recognition by science of the relations between magnetism and electricity.
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[6] Nor did La Condamine probably suspect that the small bottle of india-rubber, which he brought with him on his return from a scientific tour to America, and passed round as a curiosity to his colleagues of the French academy, was actually filled with a liquid destined to become of the most extensive application to different branches of industry; aye, a liquid without which the submarine telegraph would simply have remained an impossibility up to the present day. [↑]
[7] Such photographs have been produced in Italy since the third edition of this work appeared in the original text.
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