OF DIALING. 



389 



Let this figure represent an erect direct south-wall, on 

 which a Baby- 

 Ionian Dial is to 

 be drawn, shew- 

 ing the hours 

 from sun-rising; 

 the latitude of 

 the place, whose 

 horizon is paral- 

 lel to the wall, 

 being equal to 

 the angle K CR. 

 Make, as for a 

 common dial K G=K R (which is perpendicular to CR) 

 the radius of the equinoctial JE, Q, and draw R S per- 

 pendicular to C K for the stile of the dial ; the shadow 

 of whose point R is to mark the hours, when S R is set 

 upright on the plane of the dial. 



Then it is evident, that in the contingent line M Q, 

 the spaces K 1, K 2, K 3, &c. being taken equal to the 

 tangents of the hour-distances from the meridian, to the 

 radius K G, one, two, three, Sec. hours after sun-rising, 

 on the equinoctial day ; the shadow of the point R will 

 be found, at these times, respectively in the points 1, 

 2, 3, &c. 



Draw, for the like hours after sun-rising, when the 

 sun is in the tropic of Capricorn yf V, the like common 

 lines C D, C E, C F, &c. and at these hours the shadow 

 of the point JR will be found in those lines respectively. 

 Find the sun's altitudes above the plane of the dial at 

 these hours, and with their co-tangents S d, S e, S f, &c. 

 to radius 5 R, describe arcs intersecting the hour-lines 

 in the points d, e, f, &c. so shall the right lines 1 d, 2e, 

 3f, &c. be the lines of I, II, III, &c. hours after sun- 

 rising. 



The construction is the same in every other case, due 

 regard being had to the difference of longitude of the 



LECT. 

 XI. 



