PORTION Or THE COSMOS. THE PLANETS. 311 



corresponds to their absolute or true magnitudes, beginning 

 with the smallest : 



The group of the smaller planets, of which Pallas and 

 Vesta appear to be the largest : then 



Mercury. Neptune. 



Mars. Uranus. 



Venus. Saturn. 



Earth. Jupiter. 



At their respective mean distances from the Earth, Jupi- 

 ter has an apparent equatorial diameter of 38" 4 ; the 

 equatorial diameter of Venus, which is nearly of the same 

 magnitude as the Earth, being only 16" 9; and that of 

 Mars 5" 8. At the inferior conjunction, however, of 

 Venus, the apparent diameter of the disk increases to 

 62"; whereas that of Jupiter, when in opposition, only 

 increases to 46". It is here necessary to remark that 

 the place in the orbit of Venns at which that planet appears 

 brightest falls between its- inferior conjunction and its 

 greatest digression from the sun ; at which time the 

 narrow bow of light, by reason of its greatest proximity 

 to the Earth, gives its most intense light. On the average, 

 Venus shines brightest, and, in the absence of the sun, even 

 casts shadows when she is 40 east or west of the sun ; 

 her apparent diameter is then only 40", and the greatest 

 breadth of her illuminated portion scarcely 10' . 



Apparent diameters of 7 planets : 



Mercury, at mean distance, 6"- 7 (oscillates from 4-"4 to 12") 

 Venus 16-9 ( 9'5 ,,62) 



Mars 5-8 ( 3'3 ,,23) 



VOL. III. T 



