We know that some day the inhabitants on Mars or some other planet will want to talk to us. They have doubtless been studying us and consider us still too barbarous and primitive to be worth talking to.
But when we become semi-civilized, in the cosmic sense of the word, the older and wiser planets will get ready to open communication with us.
How will they go about it? They are perhaps absolutely different from us, in shape, in manner of thought, in every conceivable way, including language, customs, and so on.
BUT GEOMETRICAL, MATHEMATICAL FACTS ARE THE SAME THROUGHOUT THE UNIVERSE.
Will not the wise Martian who wants to speak to us and decides to flash some message down here on our clouds, or on the surface of the water, utilize the universality of geometrical truths in order to make us understand that thinking beings are trying to talk to us?
The sum of the angles of any triangle is equal to two right angles.
That is true of every triangle, no matter what its shape, no matter whether it be drawn on this earth or on the most distant sun.
Therefore, when the Martian gentleman gets ready to talk to us he need only repeatedly place before us two right angles followed by a triangle, or a triangle followed by two right angles. Instantly, like Aristippus, we can say there is civilization in Mars, or wherever that sign comes from, or at least there is organized thought. The mind that is flashing that sign knows something about geometry.
Of course, we should also recognize "signs of civilization" if the Martians should project upon our atmosphere a skeleton hanging in chains. But it is to be hoped that the Martians have got beyond that particular evidence of civilization.