It was only when my observations began in the latter half of the opposition of 1901 that, the season on Mars having so far advanced, all snow in those latitudes had melted. Then appeared, however, the canal Hippalus, an arctic canal of some importance, lying on that part of the planet previously occupied by the polar cap. When later studying the observations on the rifts I remembered this canal, and turning to the drawing made some months before to compare the two critically, discovered that the canal occupied the precise position held earlier by the rift. One had said the rift had never vanished, but that the white surrounding it had simply turned to ochre. Here, then, was a striking coincidence of place, too exact to be the result of chance. Impressed by the identity, I examined all the other rifts seen early in 1901, comparing them with the arctic canals seen later, to the finding of no less than five cases of the same coinciding positions. The importance of the identification here made of an arctic canal with a previous rift in the polar cap has led me to make a list of the canals thus identified at this opposition. ==========+===========================+============================= | VISIBLE AS A RIFT | VISIBLE AS A CANAL ----------+---------------------------+----------------------------- Hypanis | January 1 and February 4 | April 18 (?), May 20, 22, | | 27, June 4, 5, 6, 7, 8, 25 Hippalus | January 19 and February 4 | April 18, May 27 Rhombites | February 4 | May 27 Python | February 20 | March 31 Zygatis | January 18, 19 | May 7, June 3 to 8 ==========+===========================+============================= If it be asked why these canals do not appear recorded at the March presentation as either the one phenomenon or the other, the answer is twofold. First, because they showed as shadings lost amidst a shaded mass; and, secondly, the observations at several oppositions indicate a great amount of haze over the region at that season of the Martian year. We may now go back to the very first rift, that of 1897. The Martian season grew later with each succeeding opposition, and it so chanced, abetted by this fact, that the delaying snow was never seen covering that part of the planet again and so, of course, not the rift. The Martian summer in those high latitudes came on, and with it brought the great arctic canal, the Jaxartes, into conspicuousness. The canal in consequence had been observed for some time before it proclaimed itself the apotheosis of a rift and that of the first and most important rift of all. Comparison of position, however, entirely confirmed the conjecture and added another and the most striking of all to the list.