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Rh really so bad as I have made it appear to you; I have exaggerated things for the sake of plainness. One thing which helps us is that the Sun moves about, throwing shadows in different directions and of different lengths from the same mountain; so that if the supposed plain round the base slopes upward in one place and downwards in another, the lengths of the shadows will show it.

If there are mountains in the Moon like our own mountains, are there also inhabitants like those on the Earth? At the beginning of this lecture we considered the case of Mars, and I showed you how hard it would be to see any signs of life on Mars by turning things round and supposing that we were looking at the Earth from Mars. You remember that we could not see violent changes in the British Isles even with the best telescope from that enormous distance. But the Moon is much nearer to us than Mars is: only a quarter of a million miles instead of (say) 50 million. If we use a telescope magnifying 1000 times, it is as though we were looking at things with the naked eye from 240 miles