242 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1956 



Antoniadi. Very few of the canals were seen this year, when the 

 planet was farther from the earth than during the previous two 

 oppositions. 



A vast yellow cloud was seen from August 23 to 27, 1909, by An- 

 toniadi covering much of the surface around the Trivium Charontis, 

 while in December 1911 another such cloud appeared to the south and 

 southeast of Syrtis Major and could be seen changing its shape and 

 size from November 3 to December 23. This cloud stayed for a long 

 time over this part of Mars, in contrast with the majority of such 

 clouds, which usually disappear fairly quickly. It is certain that the 

 yellow and the white clouds differ in their composition, and this has 

 an effect on the length of their visibility. 



If we compare the drawings of the earlier observers, made before 

 the canals were recognized as such in 1877, we can still trace, although 

 faintly, some of the principal canals, which proves that these strange 

 features are not of recent development, but are permanent. We can 

 also find traces of clouds and other indications of variations among 

 the dark patches, showing that the weather conditions on Mars have 

 not altered appreciably during the last 100 years. 



But in addition to the temporary changes introduced by clouds, 

 we also find others which affect the dark patches, such as changes in 

 their shapes, a growing-out more than usual at this point and a with- 

 drawal at another. These changes are more interesting than those 

 due to mere clouds, as they must mean some alterations in the patches 

 of vegetation themselves. It may be that they arise from the amount 

 of sunshine at the time, coupled with temperature changes, but it is 

 not impossible that some at least are due to the activities of some other 

 form of life — that is to say, to deliberate interference with the growth 

 at the places where the changes are noted. Perhaps the soil is ex- 

 hausted in these places, with the result that vegetation fails for a time, 

 and it is not impossible that the failing is due to the excessive "reap- 

 ing" in those areas. It must be remembered that what look to us like 

 small features are in reality objects covering many square miles of 

 the only fertile areas on this otherwise arid planet. It is even possible 

 that the changes are due to the failing of some new kind of vegetation 

 deliberately introduced as an experiment. 



The last opposition of Mars took place in 1954, 2 but the planet was 

 too low in the sky for successful observations in Britain. At one time 

 it rose only 10 degrees above the southern horizon, and under such 

 conditions no useful observations could be obtained. The writer was 



* Since this was written, Mars came to opposition in 1956. The most striking 

 feature of this opposition was the excessive faintness of the markings. The 

 writer observed at Mention but only succeeded in detecting a few of the 

 "canals."— H. P. W. 



