162 OUTLINES OF NATURAL PHILOSOPHY. 



gation is to the radius, as the tangent of the 

 geocentric latitude to the tangent of the incli- 

 nation. 



LA LANDE, 1358. GREGORY'S Astron. Book in. 

 prop. 20. 



If the planet be 90 distant from the Sun, the lati- 

 tude observed is just equal to the inclination. 

 KEPLER made use of this last method for deter- 

 mining the inclination of the orbit of Mars. 



162. If an inferior planet, at the inferior and 

 superior conjunctions, or a superior planet at 

 the opposition and conjunction, be also 90 dis- 

 tant from the node ; from the observation of 

 Its geocentric place, the inclination of the or- 

 bit being known, the ratio of the planet's dis- 

 tance from the Sun, to the Earth's distance 



from the Sun, may be found. 



. 



In the annexed figure, (fig. 17,), let S be the Sun, 

 W the orbit of Venus, E the Earth ; then joining 

 EV, EV, and drawing the perpendiculars VD, 

 V'D', if ES = a, SV=&, and the angle ESV=I, 

 SD = b cos I = SD'; so that ED = a 6cosl, 

 and ED' = a + b cos I. If the angle VES = A, 

 and V'ES = *', then because VD = V'D', 



tan 



,<ro .II - 



