Apparent position* of the Simat 

 different hours of the day at the, 

 time of the ffmaeett . 



Fig;. 3. 



For some time after Sun-set, the rays 

 roll illumine the Atmosphere diffw 

 sinq tharutth'es thrnutjh space and, 

 Niyhtrome.on almost uuttnfibly. this* 

 u callftl twilight anil the dawn is 

 a similar Phenomenon which prectf 

 des Sun-rife. The So lor ray S-0. 

 whichenifrfthfAlnvisplirreat O. 

 instead of coming out at ^i will be 

 turnedafide, rejrwtrdorbKnt more 

 and more, as itpeneiratcs the vari 

 ous Strata of Air. and will at last 

 reach the Earth iliwribinii the Curve 

 O.G. The Observer atGnvuldthus 

 seethe Sun much lonperaiE thanhe 



The effect, o fthe dawn is the. reverse 

 j fthis -let the Earth be reprufcnted 

 hj-AB.C-D.and.lr.whenetJieSu/i.-rieei: 

 the horizonat H.GRm tight from 

 all parts ofthe.Hea\ -ens either directly 

 trb\- reflection. the point A at which, the 

 limhtif not actually n ftii, has above, its 

 horizon the lenticular portion oftheAfc 

 mosphere K.LR. indirectly ilhurunated, 

 the dawn if most brilliant at K . the tint 

 bewming more feeble until it reaches R. 

 '.< utmost limit aboi-e thehorujonatSi. it 



... ~.,...,andtit D where the Sun isRifiny 



thewholeofihf horizon if illuminated while at 

 C. the. lenticular portions of theHeM'ens T.3TX. 

 r v,ily-receivelight.T^e^rffntof&i^$itissht*vn, 

 onthrtiaiirebyaZoneofUghtershadethanthatwhuh' 

 , .marks Nipht . Supposed fkeNeridianof London. <fe 

 itisNoon at G. 9OWest,Long. itisB A.M.andatY. 

 4dWestLony. fl o 'dock by the effectof Atmospheric at- 



the Sun wouldappearat Y.at3o 'Clock P M . Thus -as the-Earth. 

 e3 ~orth Po le beiiuj at P. turns on itsAjds from. IVest to East, as inr 

 Jicated by the. Arrows, the Sun will appear to o ccupy the oppositepomit 

 ..]. S.E.U. This figureis drmvn at the tune whfnthfSunappears to 

 describe the Equator . 



Inclination of the Orbit to the Ecliptic 

 Mean distance from the Sun in leagues 



Sidereal revolution round the Sun 



Diameter in leag-iies 



Velocitv per minute, in leag-ues 



Time ot'rotatioii upon its axis 



MERCUHY 



7fi 



13.36l.Ofln 

 91 



1.130 

 53 



VENUS 



3' 23 

 4. H6fi. WO 



485 



Drmni* Enparrd W Ulnwrc.fmtouTillf . 



