60 TJie Realm of Nature CHAP. 



the time of any occurrence to specify by what meridian the 

 time is regulated. The local time in different parts of the 

 world at Greenwich noon is shown on Plate XIX. Greenwich 

 time is used throughout all Great Britain, although at 

 Greenwich noon it is 12-7 local time in the east of Norfolk 

 and 1 1-37 in the west of Cornwall. In Ireland, Dublin time 

 is employed, the clocks there showing 11-35 at Greenwich 

 noon. Throughout the United States and Canada the time 

 is changed by I hour at every 15 of longitude ; so that in 

 each belt of that width the same time is shown on all the 

 clocks, and between the Atlantic and Pacific there are five 

 changes of this kind. Travelling eastward or toward the sun- 

 rising has the effect of making the Sun rise earlier each day 

 and set earlier each night ; passengers on an eastward-bound 

 steamer in the North Atlantic have their meals 20 minutes or 

 half an hour earlier each day according to the speed of the 

 vessel, and the clock appears to go slow. Going right round 

 the world in an easterly direction the few minutes cut off each 

 day by meeting the Sun before the complete rotation of the 

 Earth amount to one whole day extra, so that, for example, 

 in i oo Earth rotations the traveller has seen I o i noons, and 

 recorded the doings of 101 days (each i per cent shorter 

 than a day at home) in his diary. Similarly going in a 

 westerly direction the rising and setting of the Sun are 

 delayed by an equal interval of time, and on going round 

 the world westerly in 100 Earth rotations there have been 

 only 99 noons and the doings of only 99 days recorded, 

 each " day " of course being i per cent longer than a day 

 at home. In order to keep the dates right a day is dropped 

 out of the reckoning of all vessels sailing eastward when 

 they cross the meridian of 1 80 from Greenwich, and a day 

 is added on to the reckoning when they cross the same 

 meridian bound westward. 



97. Longitude. The longitude of a place is the angular 

 distance of its meridian from some prime meridian, that of 

 Greenwich being usually adopted. In order to find the longi- 

 tude of a place from the meridian of Greenwich it is only 

 necessary to know the local time and Greenwich time at the 

 same moment. Local noon is easily ascertained by direct 



