till

A 8

T R O N O M Y.

\[\\^ na ^° >2 ‘ Hence the Days and Nightsequal, and the Sun’s Heat is now

0, at

l he §, e Angle i?C/>, which measures the-Altitude of, 4 Jn above the Horizons O, is 38° 30" — he. ,

*Ud c 'Again : When the Sun is in the Tropic T R,Wd' qucnt ly nearest to the Zenith of London , theforijj- '^nal Arch is then T I, which is longer than the6 h ln the Proportion of the Right Angle ÆNC =Mi nut rs to the obtuse Angle Æ N F = 8 Hours 16p es > N E S being an Hour-Circle drawn throughSenjj__ 0lI1 t I, and intersecting the Equator in E. TheAngj^tWnal Arch is I R, and equal in Time to the°f th e H Qj= 3 Hours 44 Minutes, the Complement*5 r er to 12 Hours.

’lastly: When the Sun appears in the SouthernA at P, and most remote from the Zenith of Lon~^tig| e ^emi-diurnal Arch is then P K, equal to thethe hp'T H I) — 3 Hours 44 Minutes nearly, equal tothe 5 §ht when the Sun was in the other Tropic ; ande qual ' Ill " n ° ( sturnal Arch K L at this Time is evidently° f he Y he Semi-diurnal Arch TI at the opposite Time

ear.

lenevcr the Sun comes upon the Line N S,

re Ptes

a s at the Hour-Circle of Six, it is then Six o’clock ,

p . ln the Summer Tropic, before Sun-set at I; andVv hen^h* : ^ e sinter Tropic, after Sun-set at K. AlsoPfes etl , e Sun comes upon the Line ZCN (which re-if is t k ' Vertical, or Azimuth of Last and West)

the En due Eaji and West, which happens at Y inhef 0re gthern Tropic, after Six in the Morning, and“°Uth e 1X the Afternoon, and vice versa at W in theI7 fropic.

a hs 0 i’ 1 is found by Observation, that the Air is notgfee s hf till the Sun is deprefs’d about 18 De-

^ !l gleAr' W ^ le Horizon, viz. at i, that is, till theto th e , z = 18° == H M j and drawing M V parallel■he Cr?*° r Zon HO, it will represent the Circle at whichK Vfi ral p . or Twilight, begins and ends, in the’^ ec iinai'° lntS w here it cuts the Parallels of the Sun's10n j as at G in the Tropic P L, and at F inN 4 the;-