VIII. IDEAS CONCERNING COMMUNICATION BETWEEN THE WORLDS CHAPTER VIII IDEAS CONCERNING COMMUNICATION BETWEEN THE WORLDS THAT in a future, which is perhaps not very far distant, say in a century or two, the inhabitants of our planet might enter into optical, electrical, or telepathic communication with those of another planet of the solar system is an event which we have some right to expect, though it is not a matter of to-morrow. About the year 1840 the astronomer von Littrow, Director of the Vienna Observatory, put forward the idea of attempting an optical communication with the Moon. A triangle traced upon the soil of the Moon by three luminous lines each from 7 to 9 miles long would be visible from here by means of our telescopes. We even observe much smaller detail, such as the singular topographical designs noticed in the lunar circle which goes by the name of Plato. Thus a triangle, a square, or circle of that size, constructed by us on a vast plain by means of luminous points, either during the day by the reflection of sunlight, or during the night by means of electric light, would be visible to the astronomers of the Moon, if such astronomers exist and if they have optical instruments equivalent to ours. The rest of the argument is of the simplest. If we observed on the Moon a correctly constructed triangle, we should be considerably interested. We should ask ourselves whether we had observed wrongly or whether an accidental geographical movement might have given rise to a regular figure. We should no doubt end by admitting that exceptional possibility. But if we suddenly saw that triangle change into a square, and some months later be replaced by a circle, we should then admit logically that an intelligent effect proves an intelligent cause, and we should think with some reason that such figures undoubtedly reveal the presence of geometers on the neighbouring world.