DISTRIBUTION OP STARS. 187 



existence of this star must therefore have reached Ptolemy 

 through the medium of those who had made voyages to the 

 southern parts of the Red Sea, or between Ocelis and the Mala- 

 bar emporium, Muziris. 85 Though improvements in the art of 

 navigation led Diego Cam, together with Martin Behaim, along 

 the western coasts of Africa, as early as 1 484, and carried Bar- 

 tholomew Diaz in 1487, and Gama in 1497 (on his way to 

 tl^e East Indies), far beyond the equator, into the Antarctic 

 Seas, as far as 35 south lat, the first special notice of the 

 large stars and nebulous spots, the first description of the 

 "Magellanic clouds" and the "coal-sacks," and even the 

 fame of " the wonders of the heavens not seen in the Medi- 

 terranean," belong to the epoch of Vincenze Yariez Pinzon, 

 Amerigo Vespucci, and Andrea Corsali, between 1500 and 

 1515. The distances of the stars of the southern hemis- 

 phere were measured at the close of the 16th and the be- 

 ginning of the 1 7th century. 66 



Laws of relative density in the distribution of the fixed 

 stars in the vault of heaven, first began to be recognized 

 when Sir William Herschel, in the year 1785, conceived the 

 happy idea of counting the number of stars which passed at 

 different heights and in various directions over the field of view, 

 of 1 5' in diameter, of his twenty-feet reflecting telescope. Fre- 

 quent reference has already been made in the present work to 

 his laborious process of " gauging the heavens." The field of 

 view each time embraced only -gnWoth of the whole hea- 

 vens ; and it would therefore require, according to Struve, 

 eighty-threee years to gauge the whole sphere by a similar pro- 

 cess. 67 In investigations of the partial distribution of stars, 

 we must specially consider the class of magnitude to which 



65 Cosmos, vol. ii. pp. 538, 539. 



86 Olbers in Schumacher's Jahrb. fur 1840, s. 249, and 

 Cosmos, vol. i. p. 51. 

 67 Etudes cVAstr. stellaire, note 74, p. 31. 



