At the canal’s maximum and minimum the equality of its two constituents is chiefly to be remarked, though it occurs on other occasions as well. But, what is significant, when the two differ it is always the same one that outdoes its fellow. It may be the right-hand twin in one pair, the left-hand one in another; but whichever it be, for the particular canal its preëminence is invariable. It is this canal which, except for adventitious help or hindrance from the air-waves, alone shows when the double assumes the seemingly single state. We may therefore call it the original canal, the other being dubbed the duplicate. In some cases it has been possible to decide which is which. It might seem at first sight as if this point should always be ascertainable. But the determination is more dilemmic than appears, not from any difficulty in seeing the canal, but from the absence of distinguishing earmark at its end. In a long stretch of commonplace coast, the precise point of embouchure of a solitary canal cannot be so certainly fixed as to be decisive later between two which show close together in the same locality. It is only where some landmark points the canal’s terminal that the problem admits of definite solution. This telltale tag may be a bay like the Margaritifer Sinus, or double gulfs like the Sabaeus Sinus, or portions of a marking not too large to permit of partitive location like the Mare Acidalium, or a canal connection like the Tacazze which prolongs the one line and not the other. In these and similar instances the two lines become capable of identification, and in such manner have been found those comprised in the following list:— ===================+===================+================ | | DATE OF DOUBLE CANAL | ORIGINAL LINE | ASCERTAINMENT -------------------+-------------------+---------------- Phison | The Eastern | 1894 Euphrates | The Western | 1894 Titan | The Western | 1896 Hiddekel | The Eastern | 1896 Gihon | The Western | 1896 Gigas | The Northwestern | 1896 Djihoun | The Western | 1901 Laestrygon | The Eastern | 1903 Nilokeras I and II | The Northern | 1903 Astaboras | The Southern | 1903 Jamuna | The Eastern | 1905 Ganges | The Western | 1905 ===================+===================+================