Among the astronomers of this period, the Landgrave of Hesse deserves particular praise, who erected a magnificent observatory at the top of the Castle of Cassel, and made many observations himself, in conjunction with Christopher Rothman and Justus Burge, concerning the place of the sun, of the planets, and of the stars.
But the person who enriched astronomy with the greatest number of facts of any modern who had yet appeared, was Tycho Brahe, a Dane of noble extraction, born in 1546, designed by his parents for the study of the law; but attracted by an eclipse of the sun in 1560, at Copenhagen, whither he had been sent to learn philosophy, he was struck with astonishment in observing that the phenomenon happened at the very moment it had been predicted.
He admired the art of predicting eclipses, and wished to acquire it. At first, for want of proper instruments, he fell into several mistakes, which, however, he afterwards corrected. Having early perceived his future improvements must depend on instruments, he caused some to be constructed larger than usual, and thus rendered more exact. On the 11th November, 1572, he perceived a new star in Cassiopeia, which continued without changing its place till spring 1574, equal in splendour to Jupiter or Venus. It last it changed colours and entirely disappeared. Nothing similar to this had been observed since the days of Hipparchus.
Tycho, in imitation of that illustrious astronomer, conceived a design of forming a catalogue of the stars. To promote his views, the King of Denmark ordered a castle to be built in Hueun, an island between Seonia and Zealand, which Tycho called Uranibourg, “the city of heaven,” and where he placed the finest collection of instruments that had ever yet appeared; most of them invented or else improved by himself. He composed a catalogue of seven hundred and seventy-seven stars, with greater exactness than had ever been done before; and constructed tables for finding the place of the most remarkable stars at any given time. He was the first who determined the effect of refraction, whereby we see the sun or any star above the horizon, before it is so in reality; as we see the bottom of a vessel when filled with water, standing at a distance, which we could not see when empty. He made several other improvements and important discoveries, which he published in a work entitled “Progymnasmata.” The labours of Tycho attracted the attention of Europe; the learned went to consult him, and the noble to see him. James VI. of Scotland, when he went to espouse the sister of Frederic, King of Denmark, paid Tycho a visit, with all his retinue, and wrote some Latin verses in his praise.
But these honours were of short continuance. After the death of his protector, King Frederic, the pension assigned him was withdrawn, and he was compelled to exile himself from his native country. Having hired a ship, he transported his furniture, books, and instruments to a small place in Hamburgh, in 1597. The Emperor Rodolphus invited him into his dominions, settled a large pension upon him, gave him a castle near Prague, to prosecute his discoveries, and appointed him Longomatus, a native of Jutland, and the celebrated Kepler, to assist him. But Tycho was not happy in his new situation; he died 14th October, 1601, repeating several times, “I have not lived in vain.”
Kepler was one of the greatest philosophers that ever lived, and ought to be considered as the discoverer of the true system of the world. He was born in Germany, at Wiel, near Wirtemberg, 27th December, 1571. He early imbibed the principles of Copernicus. After the death of Tycho, he was employed to finish the tables which he had begun to compose from his observations. Kepler took twenty years to finish them. He dedicated them to the emperor, under the title of the “Rodolphine Tables.”
Kepler united optics with astronomy, and thus made the most important discoveries. He was the first who discovered that the planets move not in a circle, but in an ellipse; and that altogether they move sometimes faster and sometimes slower, yet that they describe equal areas in equal times; that is, that the spaces through which they move in different parts of their orbit, are of equal times, though of unequal length; yet when two straight lines are drawn from the extremity of either space to the centre of the sun, they form triangles which include equal areas. He likewise demonstrated that the squares of the periodical times of the revolution of the planets round the sun, are in proportion to the cubes of their distance from him; a theorem of the greatest use in astronomical calculations: for having the periodical times of two planets given, and if the distance of one of them be known, by the rule of proportion, the distance of the other can be ascertained.
Kepler is said to have used logarithms in framing his “Rodolphine Tables.” This great man died in poverty, 15th November, 1631, at Ratisbon, whither he had gone to solicit the arrears of his pension, which had been very ill paid: he left nothing to his wife and children but the remembrance of his virtues.
Contemporary with Kepler was Galileo, born at Pisa, in Italy, in 1564; illustrious for his improvements in mechanics, for his application of the effects of gravity, and for the invention, or at least, the improvement of telescopes.
The use of spectacles, or reading glasses (convex for long-sighted; and concave for short-sighted persons,) had been invented by one Spina, a monk at Pisa, in 1290; or, as some say, by our countryman Roger Bacon. The use of telescopes or glasses for viewing objects at a distance, was invented by Zachary Janssen, a spectacle-maker, at Middleburg, or rather, as it is said, from the accidental discovery of a child. The honour of this invention is also claimed by others. It is certain that Galileo first improved them so as to answer astronomical purposes. He also first made use of the single pendulum for measuring time in making his observations; to which he was led, by considering one day the vibrations of a lamp suspended from the vaulted roof of a church. He likewise discovered the gravity of the atmosphere from the rising of water in a pump, by the action of a piston, which led the way to the invention of the barometer, by his scholar Toricelli.