THE USE OF THE TERRESTRIAL GLOBE. 311 



tioned in working any problem, the graduated edge 

 it is meant. 



If this be done at sea, and compared with the sun's 

 azimuth, as shewn by the compass, if they agree, the 

 compass has no variation in that place : but if they dif- 

 fer, the compass does vary ; and the variation is equal 

 to this difference. 



PROBLEM XXIV. 



The latitude, hour of the day, and the suns place, being 

 given ; tojind the sun's altitude and azimuth. 



Rectify the globe, and turn it until the index points 

 to the given hour ; then lay the quadrant of altitude 

 over the sun's place in the ecliptic, and the degree of the 

 quadrant cut by the sun's place is his altitude at that 

 time above the horizon ; and the degree of the horizon 

 cut by the quadrant is the sun's azimuth, reckoned from 

 the south. 



PROBLEM XXV. 



The latitude, the sun's altitude, and his azimuth being 

 given ; to find his place in the ecliptic, the day of the 

 month, and hour of the day, though they had all been 

 lost. 



Rectify the globe for the latitude and zenith,** and 

 set the quadrant of altitude to the given azimuth in the 

 horizon ; keeping it there, turn the globe on its axis 

 until the ecliptic cuts the quadrant in the given altitude : 

 that point of the ecliptic which cuts the quadrant there, 

 will be the sun's place ; and the day of the month 

 answering thereto, will be found over the like place of 

 the sun on the wooden horizon. Keep the quadrant of 

 altitude in that position, and having brought the sun's 



Note 88. By rectifying the globe for the zenith, is meant screwing 

 the quadrant of altitude to the given latitude on the brass meridian. 

 Note by the Antkor. 



