1863.] 435 



Allowing the white spaces to be land, which reflects light as the 

 moon in opposition, it seems a natural supposition that the shady 

 spaces should be called sea ; and this may be supported by the 

 obvious requirement of water somewhere on Mars, to agree with the 

 alternate gathering and melting of the snow round the poles. Still, 

 every observer remarks no small resemblance of some of these shady 

 tracts with particular parts of the unequally tinted grey surfaces of 

 the moon. A positive proof of ocean on the disk of Mars would be 

 afforded by the star-like image of the suii reflected from the quiet 

 surface*, or the more diffused light thrown back from the waves; 

 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 



* The quiet image here alluded to would not exceed ^th of a second of angle 

 at the opposition, if no allowance be made for irradiation. But much allowance 

 must be made for this. A thermometer-bulb, with diameter half an inch, reflects 

 the sun as a star visible by the eye at 25 yards' distance, the reflecting surface in 

 this case being about ^-oth of an inch in diameter, and therefore (if no irradia- 

 tion were allowed for) the angle subtended at the eye would be only about 1". 

 By employing on Mars a power of 300, the ^" becomes relatively magnified 

 to 15". 



The reflective power of water at a nearly vertical incidence is, however, so 

 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. 



