canals of Prof. Schiaparelli, though specially looked for, both during and after the opposition, could not be made out. At the very same time the canals were visible not only to Schiaparelli, but to Perrotin and Terby, and, as we shall see further on, some very remarkable phenomena connected with them were observed. At the Lick Observatory, too, they saw the canals, though they did not perceive all the details and peculiarities noted by Schiaparelli and Perrotin. How shall we account for these remarkable discrepancies? I do not for a moment think that they shake the substantial accuracy of the Italian observations. No doubt a clew to the explanation is furnished by what Schiaparelli has recently said of the difficulty of seeing the objects he has described: "On the rare days when these extremely difficult observations are possible, the period of good telescopic images does not last, ordinarily, more than two or three hours during the twilight, or the commencement of night. . . . I have found by experience, at Milan, that one can hardly hope to have an atmosphere sufficiently good during more than eight or ten evenings (during an opposition); sometimes even entire months pass without one's being able to make a satisfactory observation. Much rarer still are evenings of perfect images, those in which one can employ the whole power of an instrument like our Merz equatorial of eighteen inches."
And this is said of the Italian sky, which has long been famous for the steady views that it gives of the heavenly bodies. What could be expected, then, of the mist-haunted atmosphere of the Potomac flats through which the watchers at our Naval Observatory must strain their vision? At Mount Hamilton they have atmospheric conditions that rival those of Italy, and therefore it was to be foreseen that they could hardly fail to confirm the existence of Schiaparelli's strange markings.
It should be said, before proceeding, that while the great majority of the canals have been seen only by Schiaparelli himself and a few other observers, there are two or three which had been recognized, though not under their present designation, and perhaps not in their complete extent, before the Italian astronomer made his discovery. Notable among these is the narrow arm running out of the Kaiser Sea, or Syrtis Magna, as Schiaparelli names it, and which he calls the Nilosyrtis. Herschel, and even earlier observers, seem to have noticed this.
But the detection of the dark lines called canals was only the beginning of Schiaparelli's singular discoveries. The next development in this remarkable series of observations was the doubling of the canals. Those that he saw in 1877 were simple lines, or narrow bands, and, strange as their appearance was, the liveliest imagination could hardly have prefigured their aspect at subse-
