ASTRONOMY. Cl 



through any given place, makes with the plane of 

 the first meridian. This angle is called the Ion* 

 gitude of the place, and the diurnal motion fur- 

 nishes us with the means of determining it. It 

 is measured by the arch of the equator, inter- 

 cepted between the first meridian and the me- 

 ridian of the place, and is reckoned east or west, 

 according as the place is east or west of the first 

 meridian* 



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The ancients took for their first meridian, or that 

 from which their longitude was counted, the meri- 

 dian of the Fortunate Isles, a line passing, as they 

 conceived, through the western extremity of the 

 habitable earth. Many of the moderns have em- 

 ployed the same meridian, or rather that of the 

 Island of Ferro, one of the most westerly of the 

 Canaries. In general, however, nations employ 

 the meridian of their own metropolis, or of their 

 principal observatory ; as we do that of Greenwich, 

 the French that of Paris, &c. It has been propo- 

 sed to take the meridian of Mont Blanc as the first 

 meridian, being that of a point very remarkable 

 in the natural history of the globe. It would be 

 inconvenient, however, to take for a first meridian 

 any point where astronomical observations are not 

 constantly made. 



65. The hour, as reckoned under any two me- 

 ridians, is different, and the difference is proper- 

 tional to the difference of longitude, or the angle 



which 



