THE USE OF THE TERRESTRIAL GLOBE. 305 



LECT. 

 PROBLEM XVI. VIII.&IX 



yhe day and hour of a lunar eclipse being given ; to jind 

 .ill those places of the earth to ichich it will be visible. 



The moon is never eclipsed but when she is full, and 

 so directly opposite to the sun, that the earth's shadow 

 falls upon her. Therefore, whatever place of the earth 

 the sun is vertical to at that time, the moon must be ver- 

 tical to the antipodes of that place : so that the sun will 

 be then visible to one half of the earth, and the moon to 

 the other. 



Find the place to which the sun is vertical at the given 

 hour (by Prob. XIV.) elevate the pole to the latitude of 

 that place, and bring the place to the upper part of the 

 brazen meridian, as in the former problem : then, as the 

 sun will be visible to all those parts of the globe which 

 are above the horizon, the moon will be visible to all 

 those parts of the globe which are below it, at the time 

 of her greatest obscuration. 



But with regard to an eclipse of the sun, there is no 

 such thing as shewing to what places it will be visible, 

 with any degree of certainty, by a common globe ; be- 

 cause the moon's shadow covers but a small portion of 

 the earth's surface ; and her latitude, or declination from 

 the ecliptic, throws her shadow so variously upon the 

 earth, that to determine the places on which it falls, re- 

 course must be had to long calculations. 



PROBLEM XVII. 



To rectify the globe for the latitude, the zenith* and the 

 sun's place. 



Find the latitude of the place (by Prob. I.) and if the 

 place be in the northern hemisphere, raise the north 



Sotj 83. The zenith, in this sense, is the highest point of the brazen me- 

 ridian above the horizon ; but in the proper sense, it is that point of tiie 

 heaven which is directly verticnl to any given place, at any given in- 

 itant of time, Note by the Author. 

 JJ 



