304 FERGUSON'S LECTURES, 



vuf&ik ^ avin g found the place to which the sun is vertical at 

 '.^v^w the given hour, if the place be in the northern hemis- 

 phere, elevate the north pole as many degrees above the 

 horizon, as are equal to the latitude of that place ; if the 

 place be in the southern hemisphere, elevate the south 

 pole accordingly ; and bring the said place to the brazen 

 meridian. Then, all those places which are in the 

 western semicircle of the horizon, have the sun rising 

 to them at that time ; and those in the eastern semicircle 

 have it setting: to those under the upper semicircle of 

 the brass meridian, it is noon ; and to those under the 

 lower semicircle, it is mid-night. All those places 

 which are above the horizon, are enlightened by the 

 sun, and have the sun just as many degrees high to 

 them, as they themselves are above the horizon : and 

 this height may be known, by fixing the quadrant of 

 altitude on the brazen meridian over the place to which 

 the sun is vertical , and then laying it over any other 

 place, observe what number of degrees on the quadrant 

 are intercepted between the said place and the horizon. 

 In all those places that are 18 degrees below the western 

 semicircle of the horizon, the morning twilight is just 

 beginning : in all those places that are 18 degrees below 

 the eastern semicircle of the horizon, the evening twi- 

 light is ending ; and all those places that are lower than 

 18 degrees, have dark night. 



If anyplace be brought to the upper semicircle of the 

 brazen meridian, and the hour index be set to the upper 

 XII, or noon, and then the globe be turned round east- 

 ward on its axis ; when the place comes to the western 

 semicircle of the horizon, the index will shew the time 

 of sun-rising at that place ; and when the same place 

 comes to the eastern semicircle of the horizon, the index 

 will shew the time of sun-set. 



To those places which do not go under the horizon, 

 the sun sets not on that day: and to those which do not 

 come above it, the sun does not rise. 



