LEOT. 

 X. 



338 FERGUSON'S LECTURES. 



LECTURE X. 



THE PRINCIPLES AND ART OF DIALING. 



Prelimi- A DIAL is a plane, upon which lines. are described in 

 such a manner, that the shadow of a wire, or of the 

 upper edge of a plate stile, erected perpendicularly on 

 the plane of the dial, may shew the true time of the 

 day. 



The edge of the plate by which the time of the day is 

 found, is called the stile of the dial, which must be 

 parallel to the earth's axis ; and the line on which the 

 said plate is erected, is called the substile. 



The angle included botween the substile and stile is 

 called the elevation, or height of the stile. 



Those dials whose planes are parallel to the plane of 

 the horizon, are called horizontal dials ; and those dials 

 whose planes are perpendicular to the plane of the hori- 

 zon, are called vertical, or erect dials. 



Those erect dials, whose planes directly front the 

 north or south, are called direct north or south dials ; and 

 all other erect dials are called decliners, because their 

 planes are turned away from the north or south. 



Those dials whose planes are neither parallel nor 

 perpendicular to the plane of the horizon, are called in- 

 clining, or reclining dials, according as their planes 

 make acute or obtuse angles with the horizon ; and if 

 their planes are also turned aside from facing the south 

 or north, they are called declining-inclining, or declin- 

 ing-reclining dials. 



The intersection of the plane of the dial, with that of 

 the meridian, passing through the stile, is called the 

 meridian of the dial, or the hour-line of XII. 



Those meridians, whose planes pass through the stile, 

 and make ancles of 15, 30, 45, 60, 75, and 90 



