*HE USE OP THE TERRESTRFAl, v.i.OBE. 309 



ing on the said place, and rises and sets to it as to other LECT. 

 places on the globe. The number of natural days, or v^-^-^/ 

 complete revolutions of the sun about the earth, between 

 the two days above found, is the time that the sun keeps 

 constantly above the horizon without setting : for all the 

 portions of the ecliptic, that lie between the two points 

 which intersect the horizon in the very north, never sets 

 below it: and there is just as much of the opposite part 

 of the ecliptic that never rises ; therefore, the sun will 

 keep as long constantly below the horizon in winter, as 

 above it in summer. 



Whoever considers the globe, will find, that all places 

 of the earth do equally enjoy the benefit of the sun, in 

 respect of time, and are equally deprived of it. For, 

 the days and nights are always equally long at the equa- 

 tor : and in all places that have latitude, tlva days at 

 one time of the year are exactly equal to the nights at 

 the opposite season. 



PROBLEM XXI. 



To find in what latitude the sun shines constantly without 

 setting, for any length of time less than 182J " of our 

 days and nights. 



Find a point in the ecliptic half as many degrees from 

 the beginning of Cancer (either towards Aries or Libra) 

 as there are natural days* 5 in the time given ; and bring 

 that point to the north side of the brazen meridian, on 

 which the degrees are numbered from the pole towards 

 the equator: then, keep the globe from turning on its 

 axis, and slide the meridian up or down, until the fore- 

 said point of the ecliptic comes to the north point of the 



\uie 85. The reason of this limitation is, that 182} of our day* and 

 nights make hall" a year, which is the longest time that the sun shine* 

 without setting, even at the poles of the earlh. \uin by thv Author. 



A'o/c 8ti. A natural day contains the whole 24 hours: an artificial dkf. 

 the time that the sun is above the horizon. Ibid. 



