316 Royal Society : — 



but nothing of this sort has been placed on record, nor is there such 

 a variation in the appearance of these spaces from the centre toward 

 the edges as to give any special reason for thinking them occupied 

 by water. 



Atmospheric vicissitudes, however, appear to be recognized in the 

 somewhat variable aspect of many portions of the grey spaces ; for 

 these, though not much changed in the situation of the masses of 

 light or shade, are sufficiently inconstant in their shapes and details 

 to suggest the idea of a vaporous envelope, brooding over and 

 about some parts more than others, and variable from one epoch to 

 another. The drawings of Mr. Lockyer supply the best evidence of 

 these variations ; for Professor Phillips, except on a few occasions, 

 confined his attention chiefly to the stronger and apparently more 

 settled boundaries of light and shade. 



The tints on the body of Mars were observed by each of the 

 gentlemen named, but with different results. To Mr. Nasmyth, 

 with a large reflector, the ' land ' appeared of a decidedly red tint, 

 the 'water* green. The 'land' appeared red in some parts, but 

 bright and almost silvery in other parts, to Professor Phillips, looking 

 through his achromatic, which also showed the ' water ' of a grey or 

 greenish tint. No redness appeared in Mr. Lockyer's instrument, 

 which, like many others of excellent quality for astronomical re- 

 search, is intentionally ' over-corrected.' 



Mr. Nasmyth saw the snow-patGh on the south pole so distinctly 

 bordered, as to give him the impression of its having a cliff- 

 boundary. The south snow-patch did not appear to him to agree 

 with the south pole of the planet, but, on the contrary, to be con- 

 siderably excentric to it ; and he supposed this to be due to the 

 relative distribution of land and water, influencing the position of 

 the centre of greatest cold. Only a faint glimmering of the snowy 

 surfaces round the north pole was seen by any observer. 



On the whole, the author of this paper concluded that, over a per- 

 manent basis of bright and dusky tracts on the surface of Mars, a 

 variable envelope gathers and fluctuates, partially modifying the 

 aspect of the fundamental features, and even in some cases disguising 

 them under new lights and shades, which present no constancy,* — a 

 thin vaporous atmosphere probably resting on a surface of land, 

 snow, and water. 



Addendum. 



Since the reading of the paper the author has been enabled, by the 

 kindness of the Earl of Rosse; to examine a series of sketches of 

 Mars during the late opposition, from the great telescopes at Birr. 

 These drawings, six in number, were made on July 22, Sept. 14, 

 Sept. 16, Oct. 6„ Oct. 29, and Nov. 6. They confirm in a remark- 

 able manner the conclusions already presented by the author, and 



much reduced, that Professor Phillips found it possible, under that condition, to 

 observe the sun's image in water without a protecting dark glass. It seems pro- 

 bable, therefore, that even in very large reflectors the direct solar reflexion from 

 water on Mars would be too faint for observation. — Feb. 17, 1863. 



