152 A CENTURY'S PROGRESS IN ASTRONOMY. 



ambition was to become supercargo on one of 

 the trading expeditions sent to China ; and so 

 he learned English, Spanish, and geography. 

 But he never became a supercargo. In order 

 to be fully equipped for such a position, he 

 determined to learn how to take observations 

 at sea, and his acquaintance with observation 

 aroused a desire to study astronomy. He con- 

 structed for himself a sextant, and by means of 

 this, along with a common clock, he determined 

 the longitude of Bremen. 



Such enthusiasm could not be long without 

 its reward. For several years Bessel remained 

 a clerk, and the hours devoted to study were 

 those spared from sleep. He studied the works 

 of Bode, Von Zach, Lalande, and Laplace, and 

 in two years was able to compute the orbits of 

 comets by means of mathematics. From some 

 observations of Halley's comet at its appearance 

 in 1607, Bessel calculated its orbit, and for- 

 warded the calculation to Olbers, then the 

 greatest authority on cometary astronomy. 

 Olbers was delighted at this work, and he 

 sent the results to Von Zach, who published 

 them. The self-taught young astronomer had 

 accomplished a piece of work which fifteen years 

 before had taxed the skill and patience of the 

 French Academy of Sciences. 



