PHYSICAL ASTRONOMY. 275 



The greatest latitude which the Sun can have, is 

 equal to the horizontal parallax, multiplied into 

 the sine of the Moon's greatest latitude. This cart 

 hardly amount to a second ; it is called the men- 

 strual parallax, and was first mentioned by Mr 

 SMEATON, Phil. Trans. 1768. See also Mecanique 

 Celeste, torn. in. p. 106. 



. The place of Mars in his orbit is sensi- 

 bly affected by the action of Venus, the Earth, 

 and Jupiter. 



The principal inequality produced by Jupiter is 



25".6 sin (Long. $ Long, if) 

 + 16".8 sin (Long. $ Long, if); 



By the Earth, 7 ".2 sin (Long. Long. $ ) ; 

 and by Venus, 5'. 7 sin (Long. ? 3 Long. $). 



There are, besides these, some other small equations. 

 See DE LAMBRE'S Tables in VINCE'S Astronomy^ 

 vol. in. p. 48., &c. 



In the orbit of Mars, the eccentricity is diminishing. 

 The secular variation of the greatest equation of 

 the centre is 37". 



The annual and siderial motion of the aphelion is 

 16".75 forward, and of the node 23".25 backward. 

 These motions are chiefly produced by the three 

 planets just named. 



273, The 



