ON THE HISTORY OF ASTRONOMY. 457 



the sun ; and from a minute examination of these circumstances he calcu- 

 lated the relative distances of the planets from the sun, which till then had 

 remained unknown. In this system, every thing had the marks of that 

 beautiful simplicity which pervades all the works of nature, and which, 

 when once understood, carries with itself sufficient evidence of its truth. 

 Copernicus was born at Thorn, in Polish Prussia, in the year 1475 ; he 

 studied in Italy ; he taught mathematics at Rome, and afterwards settled 

 on a canonicate at Frauenberg, where, in 36 years of retirement and medi- 

 tation, he completed his work on the celestial revolutions, which was 

 scarcely published when he died.* 



About this time, William the Fourth, Landgrave of Hesse Cassel, not 

 only enriched astronomy by his own observations, but also exerted his 

 influence with Frederic, King of Denmark, to obtain his patronage for the 

 celebrated Tycho Brahe. Frederic agreed to give him the little island 

 Huen, at the entrance of the Baltic, where Tycho built his observatory of 

 Uraniburg, and, in a period of 21 years, made a prodigious collection of 

 accurate observations. After the death of his patron, his progress was 

 impeded, and he sought an establishment at Prague, under the emperor 

 Rudolph. Here he died soon after, at the age of 55. Struck with the 

 objections made to the system of Copernicus, principally such as were 

 deduced from a misinterpretation of the scriptures, he imagined a new 

 theory, which, although mechanically absurd, is still astronomically correct ; 

 for he supposed the earth to remain at rest in the centre, the stars to revolve 

 round it, together with the sun and all the planets, in a sidereal day, and 

 the sun to have, besides, an annual motion, carrying with him the planets 

 in their orbits. Here the apparent or relative motions are precisely the 

 same as in the Copernican system ; the argument that Tycho Brahe drew 

 from the scriptures in favour of his theory was, therefore, every way 

 injudicious ; for it is not to be imagined that any thing but relative motion 

 or rest could be intended in the scriptures, when the sun is said to move, or 

 to stand still. But in the Copernican system, there was an evident regu- 

 larity in the periods of all the planets, that of the earth being longer than 

 that of Venus, and shorter than that of Mars, which were the neighbouring 

 planets on each side ; and when Tycho imagined the sun to move round 

 the earth, this analogy w r as entirely lost. Tycho Brahe was the discoverer 

 of the variation and of the annual equation of the rnoon, the one being an 

 irregularity in its velocity, dependent on its position with respect to the 

 sun, the other a change in the magnitude of all the perturbations produced 

 by the sun, dependent on his distance from the earth. (Plate XXXVIII. 

 Fig. 529.) 



Kepler was the pupil and assistant of Tycho, whose observations were 

 the basis of his important discoveries : he succeeded him in his appoint- 

 ments at Prague, and enjoyed the title of Imperial Mathematician. Adopt- 

 ing the Copernican system, which was then becoming popular, he pro- 

 ceeded to examine the distances of the celestial bodies from each other at 

 various times ; and after many fruitless attempts to reconcile the places of 

 the planets with the supposition of revolutions in eccentric circles, at last 



* De Revolutionibus Orbium Coelestium, fol. 1543. 



