SUN-DIAt.5, 



71 



to a description of the principles of dialing, and then proceed to 

 illustrate the causes, which make the discrepancy observed between 

 the times indicated by a clock supposed to run with an uniform 

 motion, and a good sun-dial. We do this the more willingly, 

 for we intend our book to be of some advantage to the reader, and 

 we trust that after its attentive perusal, he will feel sufficiently 

 interested to either erect a good dial, or a meridian mark, in order 

 to determine his local time with something more of accuracy 

 than suffices for the ordinary wants of life. We mean by local 

 time, the correct solar time for the place, in distinction from 

 Greenwich time, or Siderial time. Chronometers, which are 

 accurate, but portable, time-keepers, are of4en set to Greenwich 

 time, L e. they are adjusted so as to show, wherever they are 

 carried, the actual time then indicated by the clock at Greenwich, 

 the difference between this and the time indicated by the clock at 

 any other place, or the local time will give, by simple inspection, 

 the difference of longitude. 



Let P A B C, be the earth, and E the position of a spectator 

 upon it, and let F G be the horizon, or a horizontal circle, and let 

 C H A be the plane of a great circle parallel to the small circle F 

 G, and let P B be the axis of the earth inclined to the diameter 



