THE MIDDLE AGES AND DURING THE REVIVAL. 57 



Harvey, discovered the VALVES OF THE VEINS a great 

 step towards Harvey's own discovery. As an astronomer 

 discovered (Aug. 1596) the variable star Mira (also called 

 o Ceti). 



1540 1 60 1. Ubaldi developed the LAWS OF THE LEVER 

 and the point of gravity his elucidation an important 

 forward step. 



1540 1603. Viete invented the mathematical SYMBOLS 

 an ingenious and most serviceable creation ; he also ap- 

 plied algebra to geometry; may be said to have preceded 

 Descartes and Newton on the road of mathematical analysis. 



1540 1603. Gilbert showed that a great many sub- 

 stances have the magnetic power of attraction when rubbed, 

 and that this attraction is stronger when the atmosphere is 

 cold and dry ; he found out the main principles of electricity 

 after countless experiments an evidence that experiments 

 were made in earnest. He should be remembered as the 

 FOUNDER of the science OF ELECTRICITY ; but he was also 

 one of the masters of the Inductive Method.* 



15451615. Porta invented the CAMERA OBSCURA, used 

 in astronomy and photography; invented also the MAGIC 

 LANTERN, which was perfected by the German Kircher, 

 some time later ; showed vision to emanate, not from the 

 eye, but from the light which comes to it comparing the 

 eye to the camera obscura. Delia Porta had also a good 

 notion of the use of two magnifying glasses, but does not 

 appear to have either made or improved telescopes, as it is 

 asserted. 



1546 1 60 1. Tycho Brahe built a magnificent observatory 

 on the island of Huen, given him by Frederick II. of 

 Denmark, where he observed the heavens night after night 

 for more than twenty-five years; he mapped 777 stars 

 (1,000 according to Brewster), and drew up the celebrated 

 RUDOLPHINE TABLES (in honour of the Emperor Rudolphus 

 II.) a work of twenty-five years' observations, the basis of 

 Kepler's labours, and one of the grandest works ever 

 composed. Tycho rediscovered the third inequality of the 

 moon the variation discovered before by Aboul Wefa; 

 * Set Appendix V. 



