Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/210

182 Trade Unions Act, 1871, further enacted that the purposes of any trade union shall, not by reason merely that they are in restraint of trade, be unlawful so as to render a member liable to prosecution for conspiracy or otherwise, or to render void or voidable any agreement or trust. The Act specifies certain agreements which may not be enforced in the courts, but which are still not to be regarded as unlawful. It also provides for the registration of trade unions. Their legal position under the criminal law, and the results of recent legislation on the subject, will be discussed under the heading. For an account of their history and economical relations see the article on.

 COMEDY.See.  COMENIUS, or, (1592–1671), a famous writer on education, and the last bishop of the old church of the Moravian and Bohemian Brethren, was born at Comna, or, according to another account, at Niwnitz, in Moravia, of poor parents belonging to the sect of the Moravian Brethren. Having studied at Herborn and Heidelberg, and travelled in Holland and England, he became rector of a school at Prerau, and after that pastor and rector of a school at Fulnek. In 1621 the Spanish invasion and persecution of the Protestants robbed him of all he possessed, and drove him into Poland. Soon after he was made bishop of the church of the Brethren. He supported himself by teaching Latin at Lissa, and it was here that he published his Pansophiæ Prodromus (1630), a work on education, and his Janua Linguarum Reserata (1631), the latter of which gained for him a great and wide-spread reputation, being produced in twelve European languages, and also in Arabic, Persian, and Turkish. He subsequently published several other works of a similar kind, as the Eruditionis Scholasticæ Janua and the Janua Linguarum Trilinguis. His method of teaching languages, which he seems to have been the first to adopt, consisted in giving, in parallel columns, sentences conveying useful information, in the vernacular and the languages intended to be taught (i.e., in Comenius's works, Latin and sometimes Greek). In some of his books, as the Orbis Sensualium Pictus (1658), pictures are added; this work is, indeed, the first children's picture-book. In 1638 Comenius was requested by the Government of Sweden to draw up a scheme for the management of the schools of that country; and a few years after he was invited to join the commission that the English Parliament then intended to appoint, in order to reform the system of education. He visited England in 1641, but the disturbed state of politics prevented the appointment of the commission, and Comenius passed over to Sweden in August 1642. The great Swedish minister, Oxenstiern, obtained for him a pension, and a commission to furnish a plan for regulating the Swedish schools according to his own method. Devoting himself to the elaboration of his scheme, Comenius settled first at Elbing, and then at Lissa; but, at the burning of the latter city by the Poles, he lost nearly all his manuscripts, and he finally removed to Amsterdam, where he died in 1671. As a theologian, Comenius was greatly influenced by Boehme. In his Synopsis Physicæ ad Lumen Divinum Reformatæ he gives a physical theory of his own, said to be taken from the book of Genesis. He was also famous for his prophecies, and the support he gave to visionaries. In his Lux in Tenebris he published the visions of Kotterus, Dabricius, and Christina Poniatovia. Attempting to interpret the book of Revelation, he promised the millennium in 1672, and guaranteed miraculous assistance to those who would undertake the destruction of the Pope and the house of Austria, even venturing to prophesy that Cromwell, Gustavus Adolphus, and Ragotski, prince of Transylvania, would perform the task. He also wrote to Louis XIV., informing him that the empire of the world should be his reward if he would overthrow the enemies of God.

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N the present article it is proposed to exhibit formulæ by means of which the orbital elements of a comet may be determined from three observations, assuming the comet to move in a parabola, an hypothesis upon which the apparent paths of the great majority of these bodies may be closely represented, appending thereto a fully worked example of the practical application of the formulæ; also to put the reader in possession of methods now employed for calculating ephemerides of the apparent positions of a comet, to assist in observation. The limits within which we are confined will necessitate reference to other works for demonstration of our formulæ, but care will be taken to name those authorities, which are not only most accessible, but by which the subject has been most clearly treated. A list of comets of short or moderate period, so far as known at present, a class which offers particular interest to the student of this branch of astronomy, will likewise be included. The method of calculating a parabolic orbit from three observations which we shall follow is the comparatively expeditious one proposed by Olbers, and demonstrated in his Abhandlung über die leichteste und bequemste Methode die Bahn eines Cometen zu berechnen, first published at Weimar in 1797, and since twice reprinted with considerable modifications and additions. The method is founded upon the principle that, if a c be the chord between the extreme positions of the comet in its orbit, and A C the similar chord of the earth's path, the radii-vectores at the middle position cut a c and A C proportionally to the times occupied in describing the arcs, a supposition which, though not mathematically exact, is but little in error if the intervals between the observations are pretty nearly equal, and the arcs described small. It may be convenient if the notation employed in the subsequent formulæ be given here, at least as regards the principal quantities entering into our calculations.