376 



Original Articles. 



LJ^iy, 



cloudy spaces would not be distinguished as such, except by the 

 general weakening of the distinctness of the outline between land and 

 sea, which yet would remain traceable in all its main features. This 

 effect has been occasionally experienced by every observer of Mars ; 

 never by any observer of the moon. Perhaps it is to some effect of 

 this kind that the comparative indistinctness of the outlines, and indeed 

 uncertainty as to the separation of the masses of land and water in the 

 southern parts of the planet, is to be ascribed. 



This uncertainty has been felt most in regard to the tracts of half- 

 lighted land spreading southward between longitudes 240° and 350° ; 

 tracts which in our drawing are partially shaded, to imply some 

 remaining doubt as to their being really land. A similar method has 

 been followed in regard to the extended tract about long. 90°, 120°, 

 and 150°, and lat. 40° south. In some drawings from Lord Eosse's 

 telescope, in 1862, examples of extremely different aspects of the same 

 part of the surface appear. About the central longitudes in the chart 

 on the 22nd July, 1862, a very broad belt of light and shade swept 

 excentrically round the south pole ; the same tract, on November 6th, 

 more resembled a very large network, and on the 6th of October it 

 was still quite different, but resembled a drawing of Mr. Lockyer's, 

 taken October 3rd. From the same great telescope, also, two draw- 

 ings were made on the 16th September and 29th October, which differ 

 much from each other, and from a drawing by Mr. Lockyer, 17th 

 September, in the space south of the equator, about longitude 240°- 

 280°. One of these drawings, September 16th, suggests, by its half- 

 circular lights and shades, the idea of a vast cyclonic movement. A 

 kind of enormous spirality also occurs in Mr. Lockyer's sketches for 

 October 3rd, suggestive more of atmospheric vicissitude than terres- 

 trial feature. 



Adopting this idea of a great change of appearance over particular 



tracts due to atmospheric variations, 

 we shall find the diversity of aspect 

 from day to day between one ob- 

 server and another, and between one 

 telescope and another, less perplex- 

 ing. 



A remarkable dark spot on the 

 equator, in long. 300° of our chart, 

 was observed by Madler, and has 

 been often seen by other and later 

 observers. It appears sometimes de- 

 tached, as in our chart ; at other 

 times, connected with the long dark 

 gulf, which extends to long. 360°. 

 The whole of this gulf is found to 

 change appearances in detail, yet not 

 so as to render in the least degree 

 doubtful the recognition of its main 

 features. The sketches opposite 

 will illustrate this : 



