12 ON FARLETON FELL 
there is neither air nor water; it is a dead mass of 
solid material, scorched by the Sun by day, held in the 
grip of appalling frost by night. The Moon was no 
doubt at some remote period of the Earth’s history 
cast off from that body, and it carried off with it a por- 
tion of the Earth’s atmosphere, or of the materials 
which later formed the Earth’s atmosphere. But the 
attraction of the Moon is so small that it was unable 
to retain these gases on its surface; they diffused into 
space, much of them returning probably to the Earth, 
leaving the Moon without any covering of nitrogen 
or oxygen or hydrogen or water vapour, and thus 
condemning it to permanent sterility. 
As regards Mercury, the planet nearest the Sun, 
conditions appear equally unfavourable. Mercury has 
ceased to revolve round the Sun, and continually 
presents one side towards that luminary. On the 
opposite side an extraordinarily low temperature pre- 
vails, low enough to solidify and bind permanently 
most of the gases of any possible atmosphere; while, 
on the other side, the very high temperature, due to 
perpetual and intense sunshine, has assisted the diffu- 
sion into space of the more volatile gases, such as 
hydrogen, which might have remained unfrozen. 
The question of life on Mars, which in many 
respects suggests conditions resembling those pre- 
vailing on our own globe, has long occupied the 
attention of men of science, among whom strong 
advocates of a Martian flora and fauna have not been 
wanting. If we may accept one of the most recent 
summaries* of the pros and cons of this question, the 
* SVANTE ARRHENIUS: ‘‘ The Destinies of the Stars.’’ Trans- 
lated by J. E. Fries. Putnam, 1918. 
