[[Categoria:Pagine che usano RigaIntestazione|Scientia - Vol. VII.djvu{{padleft:267|3|0]]gions are shown very clearly on drawings by the four observers mentioned in the first part of this paper, — Dawes in 1864, Schiaparelli in 1877 and later, Lowell in 1895 and later, and Antoniadi in the opposition just passed. Now if we compare the drawings of Beer and Mädler made with a a telescope of 4 inches aperture, with those of Dawes made with one of 8 inches, we see that the resemblance between the Lacus Solis and the head of the Sinus Sabaeus has entirely vanished, and that neither now appears as a plain circular dot. Thirteen years later, Schiaparelli with the same aperture as Dawes, showed about the same amount of detail, to which he was able to add in later years. Again Lowell in 1894 and subsequently, was able to show further detail with an aperture of 18 inches; whilst with 33 inches, in 1909, Antoniadi brought out a mass of structure in the regions which were so simple in the sight of Beer and Mädler.

Now the gradation in size from the Lacus Solis down to the smallest «oasis» of Lowell is a complete one. Dare we say, if a future development in the power of telescopes should equal the advance made from the 4-inch of Beer and Mädler to the 33-inch of Meudon, that the «oases» of Mr Lowell will refuse to yield to such improvement, and will still show themselves all, as uniform, circular spots? Translate this thought into terms of the past. Would Beer and Mädler have been justified in arguing that the apparent perfect circularity of the two «oases» which they observed, proved that they were artificial formations made circular, «for the circle is the figure which incloses the maximum area for the minimum average distance from its centre to any point situated within it?». («Mars», page 187).

Would not the answer have been valid that a spot too small to be defined must appear circular, since its minor irregularities are invisible, and that therefore the apparent circularity probably covered detail of an altogether different form? We know that it would. Yet it is that same argument in a stronger form against which Mr Lowell is contending to-day.

Beer and Mädler only drew two of these spots; Lowell shows 186. Beer and Mädler’s two spots seemed to them precisely alike; these two spots, as we see them to-day, bear not the slightest resemblance to each other. Mr Lowell’s 186 or more «oases» (with a few exceptions) appear all of the