MARS AS A WORLD, I 59 



planet which we possess are those in which the south pole 

 is exhibited. 



Many astronomers have given to us carefully finished 

 sketches of the appearance of the planet on such occasions. 

 Among these I now specially invite attention to the 

 remarkable series of drawings obtained in the opposition 

 in September, 1877, by Mr. N. B. Green, who enjoyed the 

 privilege of observing Mars under singularly favourable 

 conditions in the beautiful skies of Madeira. The tele- 

 scope he employed was a reflector of the Newtonian form, 

 with a mirror thirteen inches in diameter, figured by Mr. 

 With, of Hereford. The magnifying power he most 

 usually employed was one of about 250 diameters. In 

 Mr. Green's memoirs he gives us representations of twelve 

 of his drawings selected from a much larger number. The 

 pictures have been chosen to show the planet at intervals 

 of two hours. This arrangement secures that the plane 

 shall be displayed under every different aspect, for after 

 twelve views at intervals of two hours have been depicted, 

 the thirteenth would merely be a repetition of the first, as 

 the rotation of the planet on its axis is so nearly twenty- 

 four hours. Mr. Green also suggests the caution with 

 which all drawings of planets, and, indeed, all drawings 

 of celestial objects generally, should be received. He 

 truly remarks that " they are necessarily exaggerations. 

 When the eye has been taxed to the utmost to observe 

 the form of some delicate marking, any shade which the 

 hand could apply to a drawing, and which could be 

 trusted to remain as a memento of the observation, would 

 be far beyond the strength of the reality. But the value 

 of the representation need not thereby be unduly depre- 



