THE MIDDLE AGES AND DURING THE REVIVAL. 55 



14501506. Columbus discovered AMERICA (Oct. 12, 

 1492) ; observed the magnetic declination. 



1436 1476. Regiomontanus computed the earliest 

 EPHEMERIDES ever composed. 



1451 1504. Waltherus was the first in Europe to USE 

 CLOCKS to measure time during astronomical observations. 



14521519. Leonardo da Vinci advanced MECHANICS 

 before Stevinus and Galileo ; also chemistry ; traced the 

 origin of fossils ; strongly advocated experiments.* He left 

 fourteen valuable books on Natural Philosophy. 



1469 1524. Vasco de Gama rounded the CAPE OF 

 GOOD HOPE (discovered by DlAS in 1486), and found the 

 sea-route to the East Indies (Nov. 22, 1497). 



14701521. Magellan circumnavigated the globe (1519 

 1522), discovering Cape Horn, the Magellan Straits, the 

 Pacific Ocean, and numerous groups of islands. Magellan, 

 killed in the Ladrone Islands, had not the happiness to 

 complete the voyage ; his lieutenant, Sebastian del Cano > 

 reaped the glory of sailing round the earth first. 



1473 1543. Copernicus demonstrated the planetary 

 system, " founding his reasonings upon rigid induction. " 

 The ancient Greek astronomers seem to have guessed the 

 truth, but failed to demonstrate it. Copernicus's conviction 

 was so thorough that he predicted that we should see the 

 phases of Mercury and Venus. The Copernican system was 

 not generally accepted until Galileo. 



1486 1567. Stiefel found the germs of logarithms, the 

 shorthand of Arithmetic a discovery perfected and made 

 effectual by Napier ; invented the use of letters for unknown 

 quantities, and the sign + for plus and - for minus. 



1423 1541. Paracelsus transferred the medical science 

 from books to observation and nature, and by his public 

 lectures on medicine and chemistry, " rid Europe of humor- 

 alism, Galenism, and polypharmacy thus giving the heaviest 

 blow to the old pathology." Many of his ideas are borrowed 

 from the Arabs. He applied himself to reforming therapeutics^ 

 and based the medical art partly upon a knowledge of 

 chemistry. He was the first to lay down the problem of Life 

 * See pages 99, 104107, and Appendix IV. 



