VIEW OF GREENWICH OBSERVATORY, SHOWING THE SIGNAL-BALL AT THE 

 TOP OF THE DOME. 



LATITUDES AND LONGITUDES. 



1. Necessary to know our position on the earth. 2. Poles and equator. 

 3. Parallel of latitude. 4. Meridian of Greenwich. 5. Latitude 

 and longitude. 6. Methods of determining the latitude. 7. By the 

 sun. 8. By stars. 9. Hadley's sextant. 10. Latitude at sea. 

 11. To find the longitude. 12. Lunar method. 13. Ball signal at 

 Greenwich. 



1. BEFORE it is possible to acquire a distinct knowledge of the 

 position or distances of any bodies in the universe outside the 

 surface of the earth, it is first indispensable that we, who have 

 to make these calculations, should distinctly ascertain our own 

 position in reference tc the bodies we observe. But as our posi- 

 tion is subject to continual change, as well by reason of the 

 diurnal rotation of the earth upon its axis, on the surface of 

 which we are carried round, as by the annual motion of the globe 

 in its orbit round the sun, we are obliged as a necessary prelimi- 

 nary to analyse with accuracy all the circumstances of these 

 LARDNER'S MUSEUM OF SCIENCE, No. 5. H 97 



