the region where it occurs minutely enough for a sufficient length of time to mark the details of the process is another matter. I shall here give what I have been able to gather at the last opposition, and shall hope to add to it at the next. One element of mystery may be eliminated at the outset. The process is not so sudden as it seems. It is perceived of a sudden by the observer because of some specially favorable night. But it has been for some time developing. So much is apparent from my observations. Suggestions of duality occurred weeks before the thing stood definitely revealed. Furthermore, the gemination may lie concealed from the observer some time after it is quite complete, owing to lack of favorable atmospheric conditions. For it takes emphatically steady air to see it unmistakably.
The next point is, that the phenomenon is individual to the particular canal. Each canal differs from its neighbor not only in the distance the lines lie apart, but in the time at which duplication occurs. The event seems to depend both upon general seasonal laws governing all the duplications, and upon causes intrinsic to the canal itself. Within limits, each canal doubles at its own good time and after its own fashion. For example, although it seems to be a rule that north and south canals double before east and west ones, nevertheless, of two north
