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ARA the friendly Dey, he again set sail, and had once more approached within sight of the French coast, when a storm hurried the vessel southward, and landed him once more in Africa. Misfortune on the heels of misfortune! The old Dey had been beheaded; his brutal and sanguinary successor would have thrown Arago into the slave prison, had he not quickly and most opportunely been hung himself. After a detention of more than six months our philosopher again embarked, and with all his instruments, charts, and manuscripts, complete and uninjured, he attained the harbour of Marseilles on the 2nd of July, 1809. How perfectly must these three years of fatigue, privation, and every danger, have transformed the petulant confidence of the student into the endurance of the man! Arago returned to Paris amid the acclamations of the whole scientific societies of France; and—a thing previously unheard of—he took his seat in the Academy of Sciences at the early age of twenty-three.—II. The second great epoch of Arago's life is comparatively tranquil, extending from his election as academician, to the year 1848. During greater part of that time he presided over the management of the Observatory; and subsequently to the death of Fourier in 1830, he was Perpetual Secretary of the French Academy. The tranquillity here spoken of was indeed quite other than repose: nay, if we were asked for analogous cases—cases in which more astonishing, more unresting mental activity has been manifested, than that which characterized this long period of Arago's tranquil life, we must revert to such men as a Leibnitz, or an Alexander Humboldt, and a very few others who have taken rank in scientific history. No extensive reader can now be uncognizant of those exquisite, those generous, just, and, in the main, discriminating Eloges, or sketches of the characters and labours of great men, with which Arago continued to adorn the volumes of the Academy from 1830, almost until the year of his death. A translation of them is one of the many favours recently bestowed on the English literature, by the pen of Mrs. Sabine. "Zealous defender," says Humboldt, "of the interests of Reason, Arago often makes us feel how much nobility and gravity elevation of character can impress on every work of the intellect. When exposing the principles of science, on which he threw an admirable and persuasive clearness, the style of the orator becomes yet more expressive, inasmuch as it is distinguished by additional simplicity and precision. He then reaches what Buffon has designated 'the truth of style.'" Akin to these short but comprehensive biographies, are the multitude of treatises inserted in the "Annuaire,"—treatises on almost every department of physical science—on meteorology, magnetism, astronomy, and various special subjects,—the essays on the labours of Sir William Herschel, on the Steam-Engine, on the claims of James Watt to the discovery of the composition of water, and many others that have a permanent place in the literature of our time. Less perfect perhaps, but still extremely interesting, Arago's "Popular Lectures on Astronomy"—now published for the first time:—less perfect probably, because no lecture can be what it was, bereft of the impressiveness and the charm belonging to the presence and individuality of the speaker. In quite another sphere, Arago's activity was also incessant—we mean within the Observatory at Paris. It is no secret that the astronomical department of this institution had not kept pace, in its instrumental furnishings, with other great observatories of Europe; and, probably, the only work it could do well, was not much suited to the tastes and ambition of Arago. That its available instruments were not idle, however, is amply testified by its published records. But in this observatory, under Arago's supervision, was inaugurated a vast and regulated scheme of magnetic investigations. The labour bestowed on these was enormous, and the results of corresponding importance. First of all, the connection between the Auroras and magnetic storms was established there; and of much more consequence, the laws of the diurnal magnetic variations were distinctly laid down. But we have no space to enumerate the various successes of our philosopher in Geodesy, Climatology, improvements in instruments, &c., &c. It is essential, however, to explain some of his more remarkable positive and enduring contributions to science.—Humboldt says truly, that the years 1811, 1820, and 1824, were the proudest years of his career. It is delightful to know, and the revelation must have delighted both discoverers, that after the discord of European war had ceased, and the intercourse and interests of nations were again cemented by peace, our own Brewster had, without hint or possibility of concert, been working in the same path, and that he had discovered many of the most important of the truths that will ever illustrate the Frenchman's name. But let us specify: in the first place, Arago's name is indissolubly associated with what is technically termed rotatory magnetism, meaning the discovery of a singular sympathy between a rotatory disc of an unmagnetic metal rotated underneath a magnet, and the position of the magnet itself. The discovery was sufficiently singular to attract the attention of our best men of science:—it long occupied Herschel and Babbage: it is due, however, to our unequalled Faraday to state, that to him belongs the undivided honour of giving the true explanation of the phenomena, and of co-ordinating them with other critical facts of magnetism. Passing with the merest notice Arago's experimental deductions from Oersted's cardinal discovery of the relation between the magnetic and electric forces, such as his process of magnetization by an electric helix, we feel it needful to speak somewhat fully of his relations to the discovery of the phenomena and the confirmation of the wave theory of light. In reference to the facts and empirical laws of Polarization, we have already said, that when the long-suspended intercourse of Nations was renewed, Arago found himself in happy agreement with Sir David Brewster. Justice, however—not what the French call "patriotism"—requires us to state, that in this special line, his fertility had been largely surpassed by that of the Scottish philosopher. The great distinction of the Frenchman in optics (except, perhaps, his unquestionable right to the brilliant discovery of chromatic polarization), consists in the success which attended his efforts to elucidate those questions by which alone the relative merits of the conflicting theories of Emission and Undulation could be decided. The theories alluded to, occupy an extensive common territory; i.e., they explain equally satisfactorily a large class of optical phenomena. But there are points in which they are discrepant. For instance, according to the Newtonian theory, a ray of light ought, on passing from a rare medium into a denser one, to move more swiftly; the contrary, according to the hypothesis of Undulations. So early as 1818, Arago hit upon a method of testing this subject experimentally. His method rested on the theory of the phenomena of Interference. If one of the two rays which interfere—producing, through such interference, the system of alternately dark and bright bands,—is made to pass through a thin plate of glass, the shift in the position of these bands ought at once to indicate whether that ray has been accelerated or retarded. It is difficult now to understand why evidence of this nature was ever refused, clear as its ground appeared, and decisive as the result was on the side of the doctrine of propagation by waves. But the French philosopher did not stop, at least he did not desire to stop, with an argument resting in the least upon theory. Stirred anew, in 1835, by Wheatstone's ingenious method of measuring directly the velocity of electricity, he leaped to the idea of employing similar means of measuring directly the velocity of light. Aided by Breguet, he had almost completed a suitable apparatus, when failing health compelled him to relinquish the pursuit. But he lived to enjoy the satisfaction of knowing that the labours of MM. Foucault and Fizeau, resting on his suggestions, issued in the absolute demonstration of the truth which he had previously deduced from the phenomena of Interference. Few experimental results of recent times have had a larger influence in settling a question of theory.—It is impossible to describe here the important results deduced by experiment by Arago concerning the laws of the interference of polarized light; neither can we do more than refer to his many practical applications of such researches to the discovery of evanescent, and until then, apparently unapproachable facts connected with celestial physics.—In fine, this may justly be said:—The place of Arago in science is not the place due to discoverers of large or fundamental laws. He cannot, for instance, rank with a Fresnel. He cannot take rank with a Faraday: and there are a few much younger inquirers amongst us whose permanent place will be found higher than his. But if we estimate him by his activity, by his ingenuity and enthusiasm, by the life which his energy stirred everywhere around him, and by the importance of the theoretical consequences of his remarkable disclosures of the empirical laws of various classes of phenomena, it must be acknowledged by every impartial inquirer, that neither in previous nor in recent times, has he had many equals, certainly only few superiors.—III. It remains that we briefly sketch what may be termed the public or political life of Arago. It may be accepted,