244 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1956 



Sky and Telescope, vol. 13, No. 11. According to this account Dr. 

 McLaughlin believes that the dark areas are not caused by vegetation, 

 as most astronomers think, but are due to drifts of volcanic ash. The 

 volcanic dust originates in active volcanoes, which are supposed to be 

 at the tips of fan-shaped markings. It is suggested that the general 

 wind circulation of the planet causes the dust and ash to be deposited 

 in the places where we see the dark markings. The green color is 

 ascribed to the reaction of carbon dioxide and the scanty moisture 

 with the ferromagnesian minerals to form chlorite and epidote, which 

 are green in color. The canals Dr. McLaughlin believes to be partly 

 ash and partly volcanic rifts ; this idea was, however, suggested long 

 ago by the late Alfred Russel Wallace. 



The objection to this theory is the presumed existence of volcanoes 

 on Mars. There may be volcanoes on Mars, but that the ash or dust 

 from them would always be blown by winds to the same points on the 

 planet is a weak point unless we assume that there are certain irregu- 

 larities in the surface which also enter into the shaping of the dark 

 areas. Also, this theory does not take into account the seasonal changes 

 which affect both the dark areas and the visibility of the canal system. 



We have considered the evidence which observations have given as 

 to the presence of water on Mars, even although the indications are 

 that the amount is small. Also, the seasonal changes in the dark mark- 

 ings, their altered colors and the way in which the canals begin to 

 make their appearance as the polar caps melt, the certain if occa- 

 sional presence of clouds or at least mists on Mars, and the general 

 appearance of this most fascinating planet all combine to suggest that 

 Mars is largely a waterless desert and that the dark areas are really 

 tracks of vegetation that owes its life to what water can be conveyed 

 along the natural waterways or canals. Perhaps the future will show 

 that Lowell, with his imaginative but magnificent idea of their having 

 been dug in the past by a race of intelligent beings in a vain effort to 

 ward off the inevitable drying-up of their world, was right after all ; 

 but this is not likely to happen until the first spaceship has touched 

 down on the alien and strange landscape of the red and green planet. 

 Then will come the time when men may settle on the planet; then, 

 perhaps, the name will be changed from that of the god of war to that 

 of the god of peace, and men will live freely in their new environment. 



