OF DTALFNG. 341 



and the gnomon the earth's axis, whether it be a small LECT. 

 wire, as in the above figures, or the edge of a thin plate, ^^^ 

 as in the common horizontal dials. 



The whole earth, as to its bulk, is but a point, if com- 

 pared to its distance from the sun : and therefore, if a 

 small sphere of glass be placed upon any part of the 

 earth's surface, so that its axis be parallel to the axis of 

 the earth, and the sphere have such lines upon it, and 

 such planes within it, as above described ; it will shew 

 the hours of the day as truly as if it were placed at the 

 earth's center, and the shell of the earth were as trans- 

 parent as glass. 



But because it is impossible to have a hollow sphere 

 of glass perfectly true, blown round a solid plane; or if 

 it was, we could not get at the plane within the glass to 

 set it in any given position ; we make use of a wire- 

 sphere to explain the principles of dialing, by joining 

 24 semicircles together at the poles, and putting a thin 

 flat plate of brass within it. 



A common globe, 1 * 5 of 12 inches diameter, has generally Dialing 

 24 meridian semicircles drawn upon it. If such a globe bytliecom " 



mon terrex- 



be elevated to the latitude of any given place, and trial globe 

 turned about until any one of these meridians cuts the 

 horizon in the north point, where the hour of XII is sup- 

 posed to be marked, the rest of the meridians will cut 

 the horizon at the respective distances of all the other 

 hours from XII. Then, if these points of distance be 

 marked on the horizon, and the <jlobe be taken out of 

 the horizon, and a flat board or plate be put into its 

 place, even with the surface of the horizon ; and if 

 straight lines be drawn from the center of the board, to 

 those points of distance on the horizon which were cut 

 by the 24 meridian semicircles, these lines will be the 

 hour-lines of a horizontal dial for that latitude, the edge 



.Vote 103. These constructions, by means of the globe, must be con- 

 sidered rat'aer as illustrations of the theory of dialing, than as 

 methods which can be employed with practical advantage. 



