'The Ptolemean system was too complicated, and the new one which that great man Copernicus had proposed, following in the footsteps of Aristarchus of Samos, though there was nothing in it contrary to mathematical principles, was in opposition to those of physics, as the heavy and sluggish earth is unfit to move, and the system is even opposed to the authority of Scripture.'

URANIBORG. the heavens

-Dreyer, Tycho Brahe.

The observatory of Uraniborg - the castle of at Hveen was an extraordinary establishment. In a large square inclosure oriented according to the points of the compass, were several observatories, a library, laboratory, living-rooms and, later, workshops, a paper-mill and printingpress, and even underground observatories. The whole establishment was administered with lavish extravagance, while Tycho was neither careful of his obligations nor free from arbitrary arrogance in his personal and administrative relations. In spite of these difficulties "a magnificent series of observations, far transcending in accuracy and extent anything that had been accomplished by his predecessors" was carried on for not less than 21 years. At the same time medicine and alchemy were also cultivated.

Concerned as he was to secure the greatest possible accuracy, Tycho constructed instruments of great size; for example, a wooden quadrant for outdoor use with a brass scale of some ten feet radius, permitting readings to fractions of a minute.

The best artists in Augsburg, clockmakers, jewellers, smiths, and carpenters, were engaged to execute the work, and from the zeal which so noble an instrument inspired, the quadrant was completed in less than a month. Its size was so great that twenty men could with difficulty transport it to its place of fixture. The two principal rectangular radii were beams of oak; the arch which lay between their extremities was made of solid wood of a particular kind, and the whole was bound together by twelve beams. It received additional strength from several iron bands, and the arch was covered with plates of brass, for the purpose of receiving the 5400 divisions into which it was to be subdivided. A large and strong pillar of oak, shod with iron, was driven into the ground, and kept in its place by solid

mason work. To this pillar the quadrant was fixed in a vertical plane, and steps were prepared to elevate the observer, when stars of a low altitude required his attention. As the instrument could not be conveniently covered with a roof, it was protected from the weather by a covering made of skins; but notwithstanding this and other precautions, it was broken to pieces by a violent storm, after having remained uninjured for the space of five years. -Brewster.

A smaller but more serviceable azimuth quadrant of brass gave angles to the nearest minute. He had a copper globe constructed at great expense with the positions of some 1000 stars carefully marked upon it.

The very precision of his observations tended to confirm his scepticism of the Copernican hypothesis, as it seemed incredible that the earth's supposed orbital motion should cause no change which he could detect in the position and brightness of the stars. He was also misled by supposing that the stars had measurable angular magnitude. He was not successful in making any fundamental improvement in the relatively crude methods of time measurement, depending himself on wheel-mechanism without the regulating pendulum, and an apparatus of the sand-glass or clepsydra type.

In 1577 Tycho made observations on a brilliant comet, and drew from them important theoretical inferences; namely, that instead of being an atmospheric phenomenon, the comet was at least three times as remote as the moon, and that it was revolving about the sun at a greater distance than Venus - unimpeded by the familiar crystalline spheres. He was even led, in discussing apparent irregularities of its motion, to suggest that its orbit might be oval-foreshadowing one of Kepler's great discoveries. According to the current view of his time, comets

were formed by the ascending from the earth of human sins and wickedness, formed into a kind of gas, and ignited by the anger of God. This poisonous stuff falls down again on people's heads, and causes all kinds of mischief, such as pestilence, Frenchmen (!), sudden death, bad weather, etc. - Dreyer, Tycho Brahe.

Eleven years later Tycho published a volume on the comet as a part of a comprehensive astronomical treatise which was, however, never completed. About the same time his royal patron died, and the new administration proved less sympathetic with the great astronomer's work and less indulgent with his extravagance and personal eccentricities.

After a series of disagreements, Tycho withdrew from his observatory in 1597, spent the winter in Hamburg, and after negotiations with different sovereigns, accepted the invitation of the Emperor Rudolph to settle in Prague in 1599. Here he again organized a staff of assistants, including, to the great advantage of himself and of his science, the young Kepler, but his further progress was prematurely terminated by death in 1601, at the age of 55.

Tycho's chief services to the progress of astronomy consisted first, in the superior accuracy of his instruments and observations, heightened by repetition and systematic correction of errors; second, in the extension of these observations over a long series of years. In both respects he departed from current practice, and anticipated the modern. In point of accuracy his errors of starplaces seem rarely to have exceeded 1' to 2', and he even determined the length of the year within one second. While he recomputed almost every important astronomical constant, he accepted the traditional distance of the sun.

Kepler gave striking evidence later of his confidence in Tycho's accuracy by writing:

'Since the divine goodness has given to us in Tycho Brahe a most careful observer, from whose observations the error of 8' is shewn in this calculation, it is right that we should with gratitude recognize and make use of this gift of God. . . . For if I could have treated 8' of longitude as negligible I should have already corrected sufficiently the hypothesis. . . discovered in chapter xvi. But as they could not be neglected, these 8' alone have led the way towards the complete reformation of astronomy, and have made the subjectmatter of a great part of this work.' — Berry.