«ct. iv j DISSERTATION SECONB. 125 



astronomical instruments ; but this must not be understood 

 strictly, for some of Ptolemy's instruments, the paral- 

 lactic k for instance, were placed perpendicularly by the 

 plumb-line. 



Regiomontanus was the disciple of Purbach, and is still 

 more celebrated than his master. He was a man of great 

 learning and genius, most ardent for the advancement of 

 knowledge, and particularly devoted to astronomy. To 

 him we owe the introduction of decimal fractions, which 

 co.npleted our arithmetical notation, and formed the se<- 

 cond of the three steps by which, in modern times, the 

 science of numbers has been so greatly improved. 



In the list of distinguished astronomers, the name of 

 Copernicus comes next, and stands at the head of those 

 men, who, bursting the fetters of prejudice and authority, 

 have established truth on the basis of experience and ob- 

 servation. He was born at Thorn in Prussia, in 1473 ; 

 he studied at the university of Cracow, being intended at 

 first, for a physician, though he afterwards entered into the 

 church. A decided taste for astronomy led him early to 

 the study of the science in which he was destined to make 

 such an entfrc revolution, and as soon as he found himself 

 fixed and independent, he became a diligent and careful 

 observer. 



It would be in the highest degree interesting to know by 

 what steps he was led to conceive the bold system which 

 removes the earth from the centre of the world, and as- 

 cribes to it a twofold motion. It is probable that the 

 complication of so many epicycles and deferents as were 

 necessary, merely to express the laws of the planetary 

 motions, had induced him to think of all the possible sup- 

 positions which could be employed for the same purpose 

 in order to discover which of them was the simplest 



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