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HISTORY OF SCIENCE. 



FIG. ioo TELESCOPIC APPEARANCE OF JUPITER. 



ing four new satellites. The various other facts and methods which 

 Cassini added to astronomy would still make a long list; but we shall 

 here mention only his discovery of the zodiacal light, which presents 

 the appearance of a luminous atmosphere enveloping the sun, and 

 spread out in a lenticular form in the plane of the ecliptic. 



The English astronomer, JOHN FLAMSTEAD (1649 1719) distin- 

 guished himself by a long-continued and laborious series of observa- 

 tions, and also by some excellent treatises on astronomical theory. 

 Flamstead held the appointment of astronomer-royal, he being the 

 first to fill the office when the national Observatory at Greenwich was 

 established in 1675, some years after the foundation of the Observa- 

 tory of Paris. The purposes for which our Greenwich institution was 

 destined were of a different order from those which were aimed at in 

 the establishment of the magnificent observatory for Tycho Brahe. 

 The improvement of navigation and other purposes of practical utility 

 could only be effected by an institution provided with more ample re- 

 sources for the accurate observation and registration of astronomical 

 phenomena than any individual could attain. 



The successor of Flamstead at the Greenwich Observatory was ED- 

 MUND HALLEY (1656 1742), whose scientific career commenced at 

 an early age. While quite a young man Halley undertook to form a 

 catalogue of the stars which are too near the south pole of the heavens 



