“Fortunately for us, Mars spins upon itself, not as Mercury and Venus do, nor as the moon does in relation to the earth, but at a rate quite different from its movement round the sun. This means, of course, that we are able to see all sides of Mars. It is, indeed, an amazing thing that we can see and study and map both Poles of Mars, though no human eye has ever seen some parts of the earth. The day of Mars is only about half an hour longer than the day of the earth; in other words, the planet spins completely round on its axis in rather more than twenty-four and a half hours.

The surface of Mars is largely covered with markings which look as if they had been made on purpose. For many years people said that these markings were only imagined, but they have now been photographed. Some people think that they are what they seem to be– canals made by intelligent beings and carrying water; but before we form an opinion on this we ought to wait for much more knowledge. Only please remember one thing. The digging of a canal on Mars would be very much easier work than digging a canal of the same size on earth, because the planet’s mass is so much less than that of the earth, and in consequence it offers less resistance to lifting out the material when digging out the canal. We must just remind ourselves that Mars has two moons, and that the inner one travels round Mars about three times a day. It is possible to say ‘three times a day’ because the earth’s day and the day of Mars are just about the same.”

The Book of Knowledge: The Children’s Encyclopaedia, Volume VIII. Editors-in-chief Arthur Mee, Holland Thompson, The Grolier Society of London, 1912.

Photograph: NASA. Rocks near the Viking 1 Lander, the first clear image from the surface of Mars, July 20, 1976.