146 AJSINUAL REPORT SMITHSONIAN INSTITUTION, 1942 



To detect general evidence of life on even the nearest of the planets 

 would demand far larger telescopes than anything at present in ex- 

 istence, unless this evidence occupied an appreciable fraction of the 

 planet's surface. The French astronomer Flammarion once sug- 

 gested that if chains of light were placed on the Sahara on a sufficiently 

 generous scale, they might be visible to Martian astronomers if any 

 such there be. If this light were placed so as to form a mathematical 

 pattern, intelligent Martians might conjecture that there was intel- 

 ligent life on earth. Flammarion thought that the lights might suit- 

 ably be arranged to illustrate the theorem of Pythagoras (Euclid, I. 

 47). Possibly a better scheme would be a group of searchlights which 

 could emit successive flashes to represent a series of numbers. If, for 

 instance, the numbers 3, 5, 7, 11, 13, 17, 19, 23 ... (the sequence 

 of primes) were transmitted, the Martians might surely infer the 

 existence of intelligent Tellurians. But any visual communication 

 between planets would need a combination of high telescopic power 

 at one end and of engineering works on a colossal, although not im- 

 possible, scale at the other. 



Some astronomers — mainly in the past — have thought that the so- 

 called canals on Mars provide evidence of just this kind, although of 

 course unintentionally on the part of the Martians. Two white 

 patches which surround the two poles of Mars are observed to increase 

 and decrease with the seasons, like our terrestrial polar ice. Over the 

 surface of Mars some astronomers have claimed to see a geometrical 

 network of straight lines, which they have interpreted as a system of 

 irrigation canals, designed to bring melted ice from these polar caps 

 to parched equatorial regions. Percival Lowell calculated that this 

 could be done by a pumping system of 4,000 times the power of 

 Niagara. It is fairly certain now that the polar caps are not of ice, 

 but even if they were, the radiation of the summer sun on Mars is 

 so feeble that it could not melt more than a very thin layer of ice before 

 the winter cold came to freeze it solid again. Actually the caps are 

 observed to change very rapidly and are most probably clouds consist- 

 ing of some kind of solid particles. 



The alleged canals cannot be seen at all in the largest telescopes nor 

 can they be photographed, but there are technical reasons why neither 

 of these considerations is conclusive against the existence of the canals. 

 A variety of evidence suggests, however, that the canals are mere 

 subjective illusions — the result of overstraining the eyes in trying to 

 see every detail of a never very brightly illuminated surface. Experi- 

 ments with school children have shown that under such circumstances 

 the strained eye tends to connect patches of color by straight lines. 

 This will at least explain why various astronomers have claimed to 

 see straight lines not only on Mars, where it is just conceivable that 

 there might be canals, but also on Mecury and the largest satellite 



