INTRODUCTION. 



55 



XVII. To find the hearing of one, place from another, 

 and their angle of position. — Rectify the globe to the ho- 

 rizon of one of the places. Screw the quadrant of alti- 

 tude to the zenith point of the meridian, and make it 

 revolve till the graduated edge passes through the other 

 place. Then look on the wooden horizon for the point of 

 the compass, or number of degrees from the south, where 

 the quadrant of altitude meets the horizon, and that will be 

 the bearing of the laller place from the former, or the an- 

 gle of position souglit. 



XVIII. To find all those places on the earth to which 

 the sv.n at a given time is rising or settinff ; also wliat pla- 

 ces are then illuminated hy the sun, or in darkness; and 

 where it is noon, or midnight. — Find tlie place to which 

 the sun is vertical at the given time, and rectify ihe globe 

 to its horizon, in which state the place will be in the ze- 

 nith point of the globe. Then is all the hemisphere above 

 the wooden horizon enlightened, or in daylight, while the 

 hemisphere below the horizon is in darkness, or night ; 

 lastly, to all these places by the eastern side of the hori- 

 zon, the sun is just setting, and to those by the western 

 side, he is just rising. 



XIX. The time of a solar or lunar eclipse being given, 

 to find all those places at which the eclipse will be visible. — 

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

 time, and rectify the globe to the horizon of that place. 

 Then, by the last problem, it is evident, that if the eclipse 

 be solar, a part of it at the beginning only will be seen in 

 places which are not far above the eastern side of the ho- 

 rizon ; while, in the rest of the upper hemisphere, the 



whole of the eclipse will be visible. A part of it at the 

 end will be seen in places which are near to the lower sido 

 of the western part of the horizon. If the eclipse be lunar, 

 the moon will be in the opposite point of the ecliptic to 

 the sun, and vertical to that point of the earth which ia 

 opposite to the place to which the sun is vertical. Tha 

 eclipse, therefore, will be visible in the lower hemisphere. 



XX. To find the beginning and end of twilight, on anj 

 day of the year, for any latitude. — It is twilight in th» 

 evening from sunset till the sun is 18 degrees beloM 

 the horizon ; and in the morning from (he time the sui 

 is within 18 degrees of the horizon till the moment of 

 his rising. Therefore, rectify the globe to the given lati 

 tude, set the index of the hour-circle to 12 at noon, ant 

 screw on the quadrant of altitude. Find the point ol 

 the ecliptic which is opposite to the sun's place, am 

 turn the globe on its axis westward along with the quadrani 

 of altitude, till that point cut the quadrant in the IStl 

 degree below the western side of the horizon. The in 

 dex will then show the time of dawning in the morning 

 Next turn the globe and quadrant of altitude towards tha 

 east, till the same opposite point of the ecliptic meet the 

 quadrant the 18th degree below the eastern side of the ho- 

 rizon. The index will then show the time when twilight 

 ends in the evening. 



XXCi To rectify the globe to the present situation of the 

 earth. — Rectify the globe to the horizon of the place. Its 

 situation will then correspond to that of the earth ; and, 

 if it stand in the sun, it will be illuminated as the earth 

 is. 



Actual Position of the Eastern Continent in relation to Avurica. 



