Nor should it be assumed that these relatively slight manifestations of volcanic action are really insignificant.

As Professor Pickering shows, they may be regarded as comparable with the greatest volcanic phenomena now witnessed on the earth, and, speaking again of Plato, he says of its evidences of volcanic action: "It is, I believe, more active than any area of similar size upon the earth.

There seems to be no evidences of lava, but the white streaks indicate apparently something analogous to snow or clouds.

There must be a certain escape of gases, presumably steam and carbonic acid, the former of which, probably, aids in the production of the white markings."[19] [Footnote 19: Annals of Harvard College Observatory, vol.xxxii, part ii, 1900.] To Professor Pickering we owe the suggestion that the wonderful rays emanating from Tycho consist of some whitish substance blown by the wind, not from Tycho itself, but from lines of little volcanic vents or craters lying along the course of the rays.

This substance may be volcanic powder or snow, in the form of minute ice crystals.