20 SEASONS, LONGITUDE, ETC. 



works on navigation. But by an act of Congress, passed 

 some thirty years ago, the meridian of Washington was 

 established as the point of departure, and accordingly 

 our maps, charts, &c., have since been adapted to that 

 meridian. 



The sun passes over a degree of longitude in 4 minutes 

 the 360 in 24 hours. Thus, when we travel west, or 

 on a line with the sun, our watch is four minutes fast for 

 every 60 geographical miles we travel. If we travel east, 

 or on a line with the sun, it is four minutes slow for every 

 degree we travel. Hence, when it is noon at Greenwich, 

 that is, when the sun is on the meridian there, if we multi- 

 ply 74, the longitude of New York west from Greenwich, 

 by 4, and subtract the result from 12 o'clock M., it will give 

 the corresponding time at JSTew York. Thus, 74 x 4=296 

 minutes, which, divided by 60, gives 4 hours and 56 minutes 

 for the sun to travel from Greenwich to New York. 

 Subtracting this from 12 o'clock (the Greenwich time) 

 gives 7 o'clock and 4 minutes A.M. as the corresponding 

 time at New York. So also by reverse, when it is noon 

 at New York, it is 4 hours and 56 minutes past noon 

 at Greenwich. Hence results the following 



RULE. Multiply the number of degrees, minutes, and 

 seconds west or east of the given meridian by 4, reduce 

 the product to hours, &c., and for west longitude subtract 



