THE CONQUEST OF THE ZONES 



in the apparent position of the sun and moon as viewed 

 with modem astronomical instruments; and they can 

 by no means be ignored by the navigator who will de- 

 termine the position of his ship within safe limits of 

 error. And so it has been the work of the practical 

 astronomers to record thousands on thousands of ob- 

 servations, giving with precise accuracy the location of 

 sun, moon, planets, and various stars at given times; 

 and these observations have furnished the basis for the 

 elaborate calculations of the mathematical astronomers 

 upon which the tables are based that in their final 

 form make up the Nautical Almanac, to which we 

 have already more than once referred. 



These calculations take into account the precise 

 nature of the perturbing influences that are exerted on 

 the earth and on the moon on any given day, and hence 

 lead to the accurate prediction as to the exact relative 

 positions of these bodies on that day. Stated other- 

 wise, they show the precise position in the heavens 

 which will be held at any given time by the sun for 

 example, or by the important planets, as viewed from 

 the earth. How elaborate these computations are may 

 be inferred from the statement that the late Professor 

 Simon Newcomb used about fifty thousand separate 

 and distinct observations in preparing his tables of the 

 sun. Once calculated, however, these tables of Pro- 

 fessor Newcomb are so comprehensive as to supply 

 data from which the exact position of the sun can be 

 found for any day between the years 1200 B.C. and 

 2300 A.D., a stretch of some thirty-five centuries. 



Such a statement makes it clear how very crude and 



[39] 



