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were so intricate that it was impossible to represent them on a drawing. They were not confined to the brighter regions of the planet, or the supposed continents, but were found to be more numerous on the so-called seas. They showed no such regularity that they could be considered as channels running from one region to another. The eye could indeed trace darker streaks here and there, and some of these corresponded to the supposed channels, but they were far more irregular than the features on Schiaparelli's and Lowell's maps.

The matter was explained by Cerulli, a careful and industrious Italian observer, in a way which seems very plausible. He found that after he had been studying Mars for two years he was able, by looking at the moon through an opera glass, to see, or fancy he saw, lines and markings upon its surface similar to those of Mars. This phenomenon is not to be regarded as a pure illusion on the one hand, or an exact representation of objects on the other. It grows out of the spontaneous action of the eye in shaping slight and irregular combinations of light and shade, too minute to be separately made out, into regular forms.

The probable facts of the case may be summed up as follows:

1. The surface of Mars is extremely variegated by regions differing in shade, and having no very distinct outlines.

2. There are numerous dark streaks, generally some-