BIBLIOGRAPHY OF HERSCHEL's WRITINGS. 535 



Synopsis of the Writings of— Continued. 



Inclination of tlie axis of Mars 01° 18' to the orbit ; the node being in 



19° 28' of Pisces. 

 The analogy between Mars and the earth pointed out. 

 The bright polar spots are probably owing to the vivid reflection of 



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



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

 Of the spheroidical fm lire of Mars. 

 Observations relating to the jJolar flattening 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 telescojies employed. 



266 To avoid the corrections for i)hase, 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, aud the former result changed to 



1355 to 1272, or as 16 to 15 nearly. 



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



objectives employed. 



271 The equatorial diameter of Mai-s 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' fr«m 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 Hesult 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. 



The figure 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 tho 

 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, 



1784. 



437 A new Newtonian telescope has lately been completed, the object 



speculimi being 20 feet in focal length and its aperture 18^ 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 



order to complete the discoveries that seem to lie within the reach 



