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the sun. In the latter case it would be invisible from the earth, so that the growth would be recognised only by its larger size when it again came into sight. These caps were naturally supposed to be snow and ice which formed around the poles during the Martian winter, and partly or wholly melted away during the summer.

In 1877 commenced Schiaparelli's celebrated observations on the surface of Mars, and his announcement of the so-called canals. The latter consisted of streaks passing from point to point on the planet, and slightly darker than the general surface. Seldom has more misapprehension been caused by a mistranslation than in the present case. Schiaparelli called these streaks canale, an Italian word meaning channels. He called them so because it was then supposed that the darker regions of the surface were oceans, and the streams connecting the oceans were therefore supposed to be water, and so were called channels. But the translation "canals" led to a widespread notion that these streaks were the works of inhabitants, as canals on the earth are the works of men.

Up to the present time there is some disagreement between observers and astronomical authorities on the subject of these channels. This arises from the fact that they are not well-defined features on an otherwise uniform surface. Everywhere on the planet are found variations of shade—light and dark patches, so faint and ill defined that it is generally difficult to assign exact