PHILOSOPHICAL SOCIETY OF WASHINGTON. 115 



Mr. Farqukar also showed a proposed form of clock-face, in 

 which the hours were numbered from to 42 in two circuits, 24 

 being opposite 0, and so on. Such a clock would do for all meridi- 

 ans, but might easily be arranged to have any desired noon-time at 

 the top. 



Mr. Coffin remarked that he had failed to appreciate the im- 

 portance of standard time to the extent to which it had been fre- 

 quently advocated. If we examine the several departments, in 

 which such time is supposed to be needed, we can better deter- 

 mine in what way a requirement of that kind can be best supplied. 



In navigation the time of the prime meridian is a necessity ; and 

 this is furnished directly by chronometers regulated to that time, 

 while from astronomical observations the corresponding local time 

 may be found ; and both are involved in all questions of longitude. 

 No further standard time is needed in this department. 



The use of an astronomical ephemeris also requires the time of 

 the meridian for which it is prepared. A prime meridian common 

 to all nations is a desideratum. But at present the maritime 

 nations of Great Britain and the United States reckon longitudes 

 from Greenwich, while on some of the nautical charts of Russia, 

 Germany, and Spain, longitudes are given from Greenwich as well 

 as from the prime meridian of each respective country. Besides 

 this use of the meridian of Greenwich more general than of any 

 other meridian, the meridian of 180° E. or W. from Greenwich 

 passes near Behring Strait and through an extensive unoccupied 

 region of the Pacific Ocean, where it will be most convenient to 

 have the change of day, which is one less on the east side of such 

 meridian than on the west. Indeed, the change of longitude from 

 east to west, or the reverse, necessarily requires a change of the local 

 day. Wliere the change is made, is arbitrary. For instance, the 

 longitude 175° E. is equivalent to 185° W. ; but October 7 in the 

 first case is October 6 in the second. If such noting of the day, 

 which is as much a part of the expression of the local time as are 

 the hours and minutes, is attended to, we have the simple rule, com- 

 mon in navigation and the use of an ephemeris, " To the local time 

 add the longitude if west, subtract it if east, to obtain the corre- 

 sponding time of the prime meridian ; " and this rule includes the 

 day as well as its parts. 



Sir John Herschel and others have proposed that longitudes 

 should be reckoned westerly from to 360°. This would complicate 



