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much less of our own air between him and Mars, he was less likely to make that mistake. He concluded that there could not be very much, perhaps not more than on the Moon, which we know to be very dry indeed. He lived in a desolate little hut on the top of Mount Whitney for a considerable time to make

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these observations, but usually he lives on the top of a more comfortable mountain (4000 feet high) at the Lick Observatory. I got a pretty Christmas card from him, showing the Lick Observatory in winter with the snow on it, which I am sure he would like me to share with you. The snow is, of course, only there in winter, and rarely even then; generally the Lick Observatory has a beautiful summer climate. But there are mountains, as you all know, on which