| 60 | The Solar System |
could not account for the phenomena. For the decrease in one locality was not offset by the increase in others. As the quantity of the change, positive and negative, did not balance, the change could not be due to a shift of matter. It must, therefore, be ascribable to a transformation of matter. And the only thing of suitable conduct and proper local color to show the phenomena was vegetation. The "seas" were not seas, but probably areas of vegetation.
Oases. The next significant discovery was the detection of the oases, or small round black spots that dot the planet's surface. These were initially seen as such by W. H. Pickering, at Arequipa, in 1892. Pickering called them lakes, but for a reason which will appear later it seems more proper to consider them oases. Quite as singular a feature as the canals, they prove to be as universal a one. They are the more difficult of detection ; which is the reason they were recognized later. Schiaparelli told the writer that he had himself suspected them, but could not make sure.
Just as the canals form a mesh over the disk, so the oases make the knots where the lines of the network cross. To them, in short, the canals rendezvous. The number of lines which thus come together at one and the same point is some-