146 



U. S. COAST AND GEODETIC SURVEY. 



in the day may be avoided by using a negative Greenwich hour when 

 necessary. For example, 1922, January 1, hour, in the standard 

 time of the meridian 15° east of Greenwich, may be written as 1922, 

 January 1,-1 hour in Greenwich time, instead of 1921, December 31, 

 23 hour, as would otherwise be necessary. If a negative argument 



Fig. 25. 



is used in Table 5, the corresponding tabular value must be taken 

 with its sign reversed. For the middle of the series the nearest inte- 

 gral hour is sufficient. 



The values of /, v, ^, v', and 2p" are obtained for the middle of the 

 series from Table 6, using N as the argument. If N is between 180 

 and 360°, each of the last four quantities will be negative, but / is 

 always positive. Although Table 6 is computed for the epoch, 



