54 THE POPULAR SCIENCE MONTHLY. 



description is very striking, yet Schiaparelli does not pursue the 

 analogy. 



All of the regions which possess this semi-maritime character 

 frequently present a lighter color when viewed obliquely, or near 

 the edge of the planet's disk, than when seen near the meridian. 

 This fact seems strongly to suggest the presence of atmospheric 

 phenomena, which may change or modify the appearance of any 

 district covered by them according to the visual angle under 

 which it is observed. The reader has only to take an ordinary 

 terrestrial globe, and, supposing it to represent Mars, turn it 

 slowly around its axis, in order to perceive how the situation of 

 any region with respect to the center or the edges of the disk may 

 influence its appearance. Near the edge the surface of the planet 

 must necessarily be seen through a far greater depth or thickness 

 of its atmosphere than in the center of the disk, and, if that atmos- 

 phere contained clouds or mist, of course its opacity would be greater 

 in proportion to its greater depth, and the reflection of light from 

 the mist would give a whiter tone to the features of the planet seen 

 through it. Nevertheless, the cloud theory fails to account satis- 

 factorily for all the appearances that have been so carefully de- 

 scribed by Perrotin and Schiaparelli. Yet if it were possible for 

 us to imagine that masses of clouds of some sort could retain, for 

 considerable periods, a fixed or nearly fixed general form and posi- 

 tion in the planet's atmosphere, disappearing and reappearing in 

 the same localities according to the seasons, and occasionally ex- 

 tending their outlines or slightly shifting their positions, then we 

 might be able to account for such phenomena as those presented 

 by Libya, without recourse to such violent, extensive, and rapid 

 geological changes as would seem to be necessary to produce 

 alternate inundations and emergences of large areas of land. 



As to the nature of the canals, it is still more difficult to sug- 

 gest any satisfactory explanation. Several hypotheses have been 

 presented, none of which appears entirely to meet the case. I 

 have already remarked that there has not been lacking the sug- 

 gestion that these curious streaks represent the lines of actual 

 artificial water-courses on Mars. The straight and undeviating 

 course which they pursue might be regarded as lending some de- 

 gree of probability to such a view, but the enormous scale on 

 which they exist seems to compel the rejection of the hypothesis. 

 It is true that, if we consider only the influence of the force of 

 gravity on Mars, giants could dwell upon that planet whose 

 mechanical achievements might vastly surpass the greatest per- 

 formances of our engineers ; for a body weighing a ton on the earth 

 would weigh only seven hundred and sixty pounds on Mars, and 

 on the other hand a man on Mars possessing relatively the same 

 activity as one of us might be fifteen feet tall and strong in propor- 



