44 Some Astronomical Problems. [Sess. 



always the same face to the central luminary, making it 

 rotate on its axis once in 88 days, the period of revolution. 



Mars remains for consideration. The amount of sunlight 

 and heat received by this planet is about one-half as com- 

 pared with our earth. It rotates on its axis in 24^ hours. 

 Its volume is only - 15 and its mass 0*103 that of the 

 earth ; and here it may be observed, as a point of much 

 importance, that some astronomers and mathematicians assert 

 that unless a planet or satellite has a mass approaching one- 

 quarter that of the earth, it is not capable of holding an 

 atmosphere of its own, but that all gases will escape into 

 space. We may note that our moon, -^ of the mass of the 

 earth, certainly does not possess a trace of atmosphere. Even 

 in connection with our own earth, with its composite atmo- 

 sphere, the two lightest of the gases, hydrogen and helium, are 

 wanting. Now, during long ages hydrogen has been pro- 

 duced by volcanic agencies, and helium by the degradation of 

 radio-active substances. While these two gases are lost, the 

 other much heavier gases, argon, krypton, neon, &c, produced 

 at the same time and in the same way as helium, remain 

 as constituents of our atmosphere in measurable quantities. 

 If Mars, then, possesses an atmosphere at all, it must be of 

 very great rarity, and this seems to be substantiated by the 

 fact that on exceptionally good nights, when the air here at 

 the best-situated observatories allows for the finest seeing, 

 then all the detail which can be observed on the surface of 

 Mars comes out crisp and clean, and the much -discussed 

 " canals " can be observed to the best advautage. 



Whatever this remarkable feature on Mars may be, a little 

 consideration enables us to banish the idea that they can 

 be the work of beings of any kind having life. Our own 

 engineering undertakings are easily circumscribed by com- 

 paratively small natural obstructions, yet we are asked to 

 believe that on Mars, where the so-called canals mark out 

 nearly mathematically straight lines over the surface, that the 

 Martians have apparently overcome all difficulties of that sort 

 with an ease that is perfectly surprising. We cannot approach 

 Mars, even at the most favourable opposition, within 34 

 millions of miles. Our best telescopes, using even as high a 

 power as 2000 diameters, only bring us within 17,000 miles 



