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Rh with a margin wide enough for our telescopes on Earth to see, and they show us a "canal." From the straightness and arrangement of the sluices thus indicated Mr. Lowell infers that the 7 were made by intelligent beings in desperate need of water; so that he considers the "canals" a proof of life in Mars.

It may surprise you that, if there is really any chance of there being wide tracts of cultivated land, there should be any difference of opinion on the subject. Why can some people see them and others not? I can easily show you one reason. You see here a clear picture on the screen, but you seldom see a clear picture in a telescope because of air currents. By a little trick the lanternist will imitate some air currents for us; and now the picture instead of being clear and definite is all fuzzy, with the details blurred; then perhaps there comes over it now and then a clear moment, when you glimpse it clearly; but almost at once it blurs again, and you wonder whether perhaps after all you really did get that glimpse or whether it was a mistake. You wait for another clear moment, and get the same glimpse; that reassures you that you did see it; but the best way of removing doubt is for some one else to see the same thing. That is the way in which telescope observations are rendered difficult in a bad climate; and that is why people go up high mountains, in order to see whether they cannot reduce the air currents. Even when, like Mr. Percival Lowell, they build a big telescope in a specially good climate to study Mars, they can only grasp a few details at a time; and two pictures made at the