FOUCAULT'S PENDULUM EXPERI MENT, a curious and remarkable method in vented by Jean Bernard Leon Foucault (q.v.), of showing rotation of the earth on its axis, by observing a vibrating pendulum and his ex periment goes under the above name. In this experiment a gradual disc is seen to turn, while a pendulum freely suspended maintained its plane of oscillation. If a heavy ball is sus pended by a fine wire and set to vibrate like a pendulum, it may easily be shown, either mathematically or by experiment, that the point of suspension, with the wire and ball, may be rotated round an axis, passing along the length of the wire without interfering with the vibration. In other words, the pendu lum 'will continue to vibrate in the same plane, although the point of suspension be turned round the axis of suspension. It follows im mediately from this that if we could sus pend a pendulum at the north or south pole and set it vibrating it would continue to swing in the original plane of vibration; and as the earth is turning on its axis, a marked line on the earth's surface would appear to turn under neath the pendulum; or rather, it would seem to an observer, accustomed to feel as if the earth were at rest, that the plane in which the pendulum vibrates turns round relatively to the marked line on the earth's surface. It is easily shown that a similar phenomenon may be observed in any latitude except at the equator; the amount of rotation, however, that the plane of vibration of the pendulum seems to undergo is not so great in low latitudes as in high latitudes; but still in our latitudes rotation takes place to an extent easily observ able. The performance of this experiment re quires the greatest nicety. The pendulum is suspended on a fine wire, the support of the wire being constructed with great accuracy, so as not to interfere with the vibrations. The motion of the pendulum must be strictly con fined to one plane; and, for that reason, in setting it to vibrate the bob is drawn aside and fastened by a silk thread and when everything has come perfectly to rest the bob is released by burning the silk thread. During its subse quent motion it is protected from currents of air by glass screens. It need scarcely be re marked, however, that this experiment is noth ing more than an illustration. Our knowledge of the rotation of the earth, drawn from astronomical considerations, cannot be strengthened by it. This experiment was first made public in 1851, when it was exhibited by M. Foucault before the French Academy.
FOUCHg, foo-sha., Joseph, Du ICE OF Ontiorro, French politician and detective: b. Nantes, 21 May 1759; d. Trieste, 25 Dec. 1820. The Revolution, into which he entered with en thusiasm, found him teaching philosophy in Nantes; he became advocate and was sent to the convention by the department of Loire-In ferieure. Here he was placed on the Commit
tee for Public Eduction, voted for the death of the king and was implicated, at least nominally, in the atrocities of the period. In 1793 he was sent to the department of Nievre to take ven geance on such persons as had incurred sus picion, which he carried through with vigor. In 1794 he incurred the hatred of Robespierre, and thus had a strong stimulus to assist in his downfall. In August 1795, he was expelled from the convention and kept a prisoner till the amnesty in October. In 1796 he communi cated important information to the director Barras as to the designs of Babeuf and was rewarded in 1798 by being sent to Milan as Am bassador to the Cisalpine Republic. Here he labored with General Brune to establish a second 18th Fructidor; both were in conse quence recalled. He appeared in Paris in 1799, after Barras had gained the ascendency, and was appointed Ambassador to Holland. Shortly after Fouche was recalled and named Minister of Police. This post he held, with intervals, until 1815. Here he first had full opportunity to his great talents and exercise an important influence on the internal policy of France. .His elaborate system of espionage gave him great power and proved at times almost intolerable to Napoleon, who dismissed him in 1802, and rewarded him with a senatorship; but he was recalled. After the battle of Waterloo, Fouche urged Napoleon's second abdication and advised him to seek an asylum in the United States. He placed him self at the head of the provisional government, negotiated the capitulation of Paris, obtained the removal of the army behind the Loire and thus prevented useless bloodshed. Louis XVIII made him again Minister of Police; and he labored so zealously in favor of moderate measures as to incur the hatred of all the ultra royalists. He therefore resigned his office in 1815 and went as French Ambassador to Dresden. As he was struck at by the decree issued in 1816 against the murderers of the king, he sought an asylum in Prague. He afterward went first to Lintz, and then to Trieste.
Adroit, skilful, politic and unscrupulous, a Jacobin and the persecutor of Jacobins, Repub lican, Bonapartist or Royalist as the occasion demanded, Fouche loved intrigue for its own sake; from first to last he fought for his own hand and was carried through all the dramatic and startling changes of the stirring times in 'which he lived without hurt to his own person by sagaciously preparing a line of retreat for himself under all eventualities and by an in stinct of self-preservation that amounted al most to genius. The volumes of memoirs pub lished posthumously under his name have been pronounced forgeries by his family. Consult Martel, 'Etudes revolutionnaires: Etude sur Fouche' (1819); and his life by Madelin (2 vols., Paris 1901).