"Indeed, I don't," M'Allister replied; "I'm thinking it will prove the very best thing I've done in my life." "Well, sir," said Merna, "I told you those machines would suit you as an engineer; are you satisfied now you have seen them?" "More than satisfied," answered M'Allister; "they are the most extraordinary and most ingenious machines I ever saw, and I wouldn't have missed them for anything!" At the sides of each high-level canal we saw a series of locks and weirs so constructed that vessels can pass on, in successive stages, from the high-level to the low-level canals, and _vice versâ_. These locks and weirs are all within the area enclosed by the embankments forming the carets, which accounts for the long and extensive space the latter cover, as the locks are necessarily a considerable distance apart from each other to allow for a length of canal to be traversed before the next lock is reached. They are, however, not in themselves sufficiently conspicuous to be separately discerned from the earth by our telescopic observers. Machinery for forcing the water along the canals is also provided at most of the junctions everywhere on the planet. In this connection it must be remembered that the water is carried by the canals from one hemisphere to the other, and, after passing the equator, must therefore move in a direction contrary to that of ordinary gravitation. Thus at one season of the year the water passes from the north polar regions down into the southern hemisphere, and at the opposite period of the year it is carried in the same way from the south polar regions right into the northern hemisphere. Gravitation being almost non-effective as regards the flow of water on Mars, the movement would be extremely slow everywhere were it not for the machinery, which adds to the speed of the flow. The average rate of the movement of the water in the canals is about fifty-one miles a day, and it takes about fifty-two days for the water to pass from about latitude 72° down to the equator, a distance of 2650 miles. This rate of flow, as indicated by the darkening arising from the growth of vegetation which follows the flow of the water down the canals, has been observed and noted many times at Flagstaff Observatory. It was now perfectly clear to us why the "carets" are only seen in the particular places in which they have been observed by Professor Lowell and his colleagues. They are, in fact, only needed in connection with water-lifting apparatus, and locks and weirs, at the places where high-level canals connect with those at a lower level! We were all very pleased at finding the solution of a problem which had been much discussed between us without arriving at any satisfactory conclusion.