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138 occasion was the setting up of the great Nice glass of twenty-nine inches aperture. In spite of the great size of the glass, however, a first attempt resulted in nothing but failure. So, later, did a second, and Perrotin was on the point of abandoning the search for good, when, on the 15th of the month, he suddenly detected one of the canals, the Phison. His assistant, M. Thollon, saw it immediately afterward. After this they managed to make out several others, some single, some double, substantially as Schiaparelli had drawn them; the slight discrepancies between their observations and his being in point of fact the best of confirmations.

Since then, other observers have contrived to detect the canals, the list of the successful increasing at each opposition, although even now their number might almost be told on one's hands and feet.

The reason that so few astronomers have as yet succeeded in seeing these lines is to be found in our own atmosphere. That in ordinary atmosphere the lines are not easy objects is certain. A moderately good air is essential to their detection; and unfortunately the locations of most of our observatories preclude this prerequisite. Size of aperture of the telescope used is a very secondary matter. That Schiaparelli discovered the canals with an 8 1/3-inch glass, and that the 26-inch glass at Washington