340 



FERGUSON'S LECTURES. 



LECT 

 X. 



To con- 

 struct an 

 erect de- 

 clining 

 dial. 



plane equal to the co-latitude of the place. As the sun 

 / can shine no longer on this dial, than from six in the 

 morning until six in the evening, there is no occasion 

 for having any more than twelve hours upon it. 



To make an erect dial, declining from the south towards 

 the east or west. Elevate the pole to the latitude of your 

 place, and screw the quadrant of altitude to the zenith. 

 Then, if your dial declines towards the east (which we 

 shall suppose it to do at present) count in the horizon 

 the degrees of declination, from the east point towards 

 the north, and bring the lower end of the quadrant to 

 that degree of declination at which the reckoning ends. 

 This done, bring any particular meridian of your globe 

 (as suppose the first meridian) directly under the gradu- 

 ated edge of the upper part of the brazen meridian, and 

 set the hour-index to XII at noon. Then, keeping the 

 quadrant of altitude at the degree of declination in the 

 horizon, turn the globe eastward on its axis, and observe 

 the degrees cut by the first meridian in the quadrant of 

 altitude (counted from the zenith^ as the hour-index 

 comes to XI, X, IX, 8cc. in the forenoon, or as 15, 30, 

 45, &c. degrees of the equator pass under the brazen 

 meridian at these hours respectively ; and the degrees 

 then cut in the quadrant by the first meridian, are the 

 respective distances of the forenoon hours from XII on 

 the plane of the dial. Then, for the afternoon hours, 

 turn the quadrant of altitude round the zenith until it 

 comes to the degree in the horizon opposite to that 

 where it was placed before ; namely, as far from the 

 west point of the horizon towards the south, as it was 

 set at first from the east point towards the north ; and 

 turn the globe westward on its axis, until the first me- 

 ridian comes to the brazen meridian again, and the hour- 

 index to XII : then, continue to turn the globe westward, 

 and as the index points to the afternoon hours, I, II, III, 

 &c. or as 15, 30, 45, &c. degrees of the equator pass 

 under the brazen meridian, the first meridian will cut the 



