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P A P E Pv S, 



165 



talnlyacircumflancethat could bcmore eafily judged of as 

 to tune, than the completion of a fmal! thread of the Sun's 

 light, ahnoft in the horizon. 



^ But, before I proceed to draw the conclufions, although 

 It may be unnecefFary to perfons verfed in aftronomical 

 lubjeas and calculations, yet to the generality of thofe 

 who may be readers of the tranfadlions of an American 

 Plulofophical Society, and partigularly the youth in our 

 different feminaries of learning, it may be acceptable to 

 fhew the whole procefs by which the conclullons are ob- 

 tained, and how to calculate the effed which the parallax 

 es of Venus from the Sun have, both in latitude and lon- 

 gitude, with refpea to the contads here and in Furope 

 It need hardly be obferved that the true place of a planet 



in the heavens, Venus for inftance, is that where Ihe 

 would be feen if viewed from the center of the earth; and 

 that unlefs ihe is in the fpedator's * zenith, her apparent 

 place will be lower than her true place. This difference 

 of place is called the planet's parallax in altitude, and is 

 meafured in a vertical circle; being greatefl in the hori- 

 zon, and decreafing at the altitudes increafe, till in the 

 zenith it becomes nothing. The method of determining 

 the quantity of this parallax at different altitudes, and of 

 reducing into thofe of latitude and longitude, fo as to know 

 their effcdl: on the planet's place, is as follows. 

 _ Let V. (Plate 111. Fig. 7,) be the place of the Sun and 

 Venus; ZV, a vertlcle circle; EC, the ecliptic, PVD, a 

 circle of declination; OVN, part of the orbit of Venus; 

 and C, the firft point of Aries. 



Thenthefollowing things are known, viz; 



ZP, the co-latitude; VD, the declination; VP, its 

 compliment; CV, the Sun's longitude; CD, the ri<-ht 

 afcenfion; and ZPV, the hour angle from noon. 



From thcfe data, the parallaxes of Venus from the Sun, 

 namely VL, in the vertical, VN, in longitude, and LN* 

 in latitude, may be found for any given place and time. 



Vol. T. 



Y 



Let 



^iI JobMor!^'^ ^oT r" ?=■' H '"' ''^ Mr.^.^„»,;„ ;j^, in hi. account of the ITov.. 

 (icucc UDicnatioi];^, Qi. 104.; need notbc icpi;utcti ht-re. 





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