168 NOTES ON MARS. 



Whether the optical theoiy accounts for all the variations, including 

 those of the polar caps, the future must decide. Most interesting- is 

 Cerulli's appeal to the past history of areography, referring to Flam- 

 marion's valuable collection of drawings, all carefully copied from 

 originals, in his Planete Mars. Here we may see now in the tirst 

 rude telescopes impressions of Martian markings were summed up in 

 one large round spot, or one wide band, whicli latter was b}^ Cassini 

 and some others seen double. By degrees the easiest features of the 

 Southern Hemisphere were distinguished, but appeared so variable 

 that an atmospheric origin was ascribed to them. It is particularly 

 instructive to compare Knott's drawing of November 3, 1862, with 

 Lord Rosse's of three days later. Knott's telescope was of 7^-inch 

 aperture, and the features which in the 6-foot Rosse reflector appeared 

 as large dark patches on a fainter background he portrays as narrow 

 lines on white — canals on a large scale. Again, in two excellent draw- 

 ings by Kaiser, a broad band where we now recognize Praxodes, seen 

 at the opposition of 1862, becomes, six weeks later, when seeing w^as 

 more difficult, two narrow bands with faint shadings between. Other 

 examples of gemination in lines and in spots, contractions and enlarge- 

 ments, etc., may be traced, and through all the series there is a 

 remarkable, but in no wise astonishing, variety of representation. 

 One has but to consider the fugitive faintness of the objects, the im- 

 perfections of the instruments, and the personalit}^ of the observers, 

 which affects not only their vision but their mode of portrayal. On 

 this last point, which comes out verj' clearly on an examination of the 

 illustrations in La Planete Mars, Signor Cerulli has not perhaps laid 

 enough stress, nor on the influence of unconscious imitation. 



Mr. Green, the artist astronomer, used to insist on the importance 

 of the trained hand as well as the trained eye in order to obtain true 

 pictures of planetary detail. 



Is the history of discovery with regard to the large markings in 

 Mars's southern hemisphere repeating itself now with the more deli- 

 cate shadings in the northern? And with better optical means would 

 they also lose their misleading appearance of mathematical regularity 

 and their instabilit}' ? 



The artificial origin of the Martian "canals" can hardly be main- 

 tained now that they have been seen to traverse the polar ctips and to 

 appear in Venus, Mercury, and two of the Jovian satellites. On the 

 optical hj-^pothesis, on the other hand, this is precisely what we might 

 expect. It is perhaps going too far to suggest that the bands of Jupiter 

 and their varying appearances are strictly analogous to canals, since 

 their atmospheric origin is rendered probable by other considerations, 

 notably by the planet's low density; yet there is certainly a startling 

 resemblance between some early drawing-s of Mars and recent diagrams 



