BIBLIOGRAPHY OF HERSCHEL's WRITINGS. 535 



Herschel W.: Synopsis of tue Writings of— Continued. 



A. D. Vol. p. 



1784 74 259 Inclination of the axis of Mars 61° 18' to tbo orbit; the node being m 



19° 28' of Pisces. 

 260 The analogy between Mars and the earth pointed out. 



260 The bright pohir spots are probably owing to the vivid reiiection of 



light from frozen regions, and the reduction [in size] of these spots 

 is to bo ascribed to their being exposed to the sun. 



261 Of the spheroidical figure of Mars. 



262 Observations relating to the polar fattening of Mars. 



These all show a difference' in the polar and equatorial diameters; 

 even when the mirrors of the telescopes are turned 90^ in their 

 tubes, and various telescopes employed. 



266 To avoid the corrections for phase, the -measures taken on the day of 



opposition will be adopted, these having been satisfactory. 



267 The equatorial diameter of Mars is to the polar as 1355 to 1289. 



268 Corrections to this ratio considered, and the former result changed to 



1355 to 1272, or as 16 to 15 nearly. 



270 This difference does not depend on distortions from the eye-pieces or 



objectives employed. 



271 The equatorial diameter of Mars at distance 1 is 9" 8'". 



271 The atmosphere of Mars. Dr. Smith reports an observation of Cas- 



siNi's where a star about to be occulted by Mars became extremely 

 faint 6' fi-em the disk of the planet. 



272 Observations by Herschel of faint stars near Mars, which show them 



not to be more affected than the nearness of its superior light would 

 warrant. 



273 From other phenomena it appears, however, that this planet is not 



without a considerable atmosphere; for besides the permanent spots 

 on its surface I have often noticed changes in both bright and dark 

 belts, and these alterations we can hardly ascribe to any other cause 

 than the variable disposition of clouds and vapors floating in the 

 atmosphere of that planet. 

 273 Besult of the contents of this paper : 



The axis of Mars is inclined to the ecliptic 59° 42'. 



The node of the axis is in 17° 47' of Pisces. ^^ 



The point Aries on the Martial ecliptic answers to our 19° 28 of 

 Sagittarius. ■ i v 



The iif^ure of Mars is that of an oblate spheroid whose equatorial di- 

 ameter is to the polar one as 1355 to 1272, or as 16 to 15 nearly 



The equatorial diameter of Mars reduced to the mean distance of the 

 earth from the sun is 9" 8'". 



And that planet has a considerable but moderate atmosphere, so that 

 its inhabitants probably enjoy a situation in many respects similar 

 to ours. 



[Dated] Datchet, Dec. 1, 1783. 



1784 74 437 Account of some observations tending to investigate the construction of the 



heavens. By William Herschel, Esq., F. R. S. Read June 17, 



17ft4 



437 A new Newtonian telescope has lately been completed the object 



speculum being 20 feet in focal length and its aperture 18ft inches. 



It is mounted in the meridian and gives positions only in a coarse way 



437 It would perhaps have been more eligible to have waited longer in 



oTder to complete the discoveries that seem to lie withm the reach 



