Keokuk

Keokuk (The Gate City), an important commercial centre, being the capital of Lee County, Iowa, U.S.A., is situated on high ground above the Mississippi, 2 miles N. of the confluence of the Des Moines river. Seven railways meet here, and a canal to avoid the rapids secures convenient water carriage, and so a great business in pork and other western products has grown up in the last fifty years. It is built chiefly of brick, and has spacious streets, fine public buildings, and a medical school.

Eepler, John, was born of noble but needy parents at Weil, a little town of Wurtemberg, in 1571. He was a delicate seven-months' child; but in spite of disease and family troubles, he acquired some rudiments of learning, and the Duke of Wiirtemberg sent him to school, whence he passed to the university of Tubingen. Here he fell under the influence of Moesthin, a strong Copernican, and wrote a treatise to prove the diurnal rotation of the earth upon its axis. In 1593 he became Professor of Astronomy at Gratz, and, his attention being directed to the apparent want of any system in the relative size of the planets and their orbits, he spent some years in fruitless endeavours to determine the ratios that they bore to one another. The rather fanciful results of his investigations were published in 1596, and attracted the notice of Galileo and Tycho Brahe, the latter of whom offered him a sort of partnership at Prague, the Emperor Rudolph of Austria guaranteeing the expenses. The two then set about compiling the Rudolphine Tables; but Tycho died, and the Imperial promises were not kept, so that Kepler reverted to his former labours, and brought out in 1609 his Astronomia Nova, in which, from his observations of the planet. Mars, he deduces that the orbit is elliptical, and that the radius-vector between the sun and the planet describes equal areas in equal times. In 1619 he gave to the world his third and most important law - viz., that the squares of the periodic times are proportional to the cubes of the mean distances between the planets and the sun. The Harmonia Mundi, enunciating this discovery, was dedicated to James I. of England, who in vain invited him to cross the seas. War, sickness, and the difficulty of getting his salary made his life wretched, and the death of his wife just as he obtained a professorship at Linz added fresh troubles. He worked on, however, effecting great improvements in the Galilean telescope, and bringing out in 1618 the first part of his Epitome Astronomica Copernicana, followed in 1628 by the Rudolphine Tables. The Duke of Friedland now became his patron, and he settled with his new wife at Sagan, filling the chair at Rostock. A journey to Ratisbon in 1630, in the hope of recovering the arrears of salary, brought on a fever, and he died of an abscess on the brain. Kepler's work amounted to thirty-three printed and twenty-two manuscript volumes, touching upon and illuminating every branch of cosmical science. .

Eepler's Laws relate to the motions of the planets. The first two appeared in one of his writings published in 1609 at Prague, and the third one in 1619 at Augsburg. 1. The planets move in elliptical orbits with the sun in one focus. 2. In the motion of a planet round the sun the radius vector (the line drawn from the sun to the planet) sweeps out equal areas in equal times. From this it follows that the velocity of the planet must be greater when it is nearer to the sun than when it is farther off. 3. With regard to different planets, the squares of their periodic times (the times taken to go once round their orbits) are proportional to the cubes of their mean distances from the sun the mean distance from the sun being taken as half the length of the major axis of the ellipse. Since the discovery of the universal law of gravitation, Kepler's second and third laws have been mathematically deduced from the first. Previous to the time of Kepler it had been considered that the planets moved in circles round the sun with uniform velocity; hence these brilliant discoveries practically formed the basis of modern astronomy.