various regions which could be detected with sufficient certainty. But at the memorable opposition to which we have referred, the distinguished Italian astronomer discovered that the tracts generally described as "continents" on Mars were traversed by long, dark "canals," as he called them. They must have been each at least sixty miles wide, and in some cases they were thousands of miles in length. Notwithstanding the dimensions to which these figures correspond, the detection of the Martian canals indicates one of the utmost refinements of astronomical observation. The fact that they are so difficult to see may be taken as an illustration of what I have already said as to the hopelessness of discerning any object on this planet unless it be of colossal dimensions.
It is impossible to doubt that considerable changes must be in progress on the surface of Mars. It is true that, viewed from the distance at which we are placed, the extent of the changes, though intrinsically vast, seem relatively insignificant. There is, however, too much testimony as to the changes to allow of hesitation. As an illustration of what is meant, we may refer to the subsequent observations of the canals made by Schiaparelli, their discoverer. During the opposition of 1881 and 1882, he again recognised the presence of these curious objects, but it would seem that a very extraordinary transformation had taken place in some of them. They had become doubled. In certain cases a pair of canals could be detected, separated by an interval of two hundred miles or more, and running parallel to each other throughout their whole length. Again, in the opposition of 1888, other astronomers, notably Dr. Terby and M. Perrotin, have also made observations confirming the remark-
