We passed through the whole length of the Eumenides-Orcus, from its starting-point on the Phoeniceus Lacus, in the southern hemisphere, to the Trivium Charontis, in the northern hemisphere--a distance of 3540 miles, this being the longest canal on the planet. We visited the Solis Lacus, or "Lake of the Sun" (an area larger than England), situated in the southern hemisphere, which has usually been seen by our observers as a large dark patch, oval in shape. Indications of changes in this area were, however, noted at the time of the opposition in 1907; and it is not improbable that further alterations will be seen shortly. Numerous important towns exist upon this area, and several canals connect it with surrounding areas. We visited the north pole in our air-ship, and saw the snow falling thickly, and rapidly adding to the size and thickness of the snow-cap, it being winter time. We visited the south pole and watched the fast-melting snow (the cap being almost at its minimum size) and the distribution of the resultant water down the various broad channels which conduct it to the canals, from whence it is carried all over the planet. When it is spring in the northern hemisphere the winter snow-cap at the north pole will begin to melt in like manner, and the water be distributed in a similar way. The melting begins about the 1st April and lasts till July, and sometimes considerably later in the year. Thus, during the Martian year there are two distributions of water--one from the north pole and one from the south pole; and the growth of vegetation follows the passage of the water as it flows downwards from the poles to the equator. On our earth vegetation progresses in an exactly opposite direction. Beginning near the tropics, where it is always summer, as the sun passes northward of the equator so vegetation gradually appears and develops onwards towards the north pole. It is exactly the same in the southern hemisphere; after the sun crosses the equator into the south the vegetation grows and spreads towards the south pole. The reason of this is that on the earth the supply of water by rainfall and snows is abundant, and it only requires the warmth of the sun to cause vegetation to spring up again at the proper season when the winter has passed. On Mars the sun has the same action, but until the water comes down from the poles and furnishes the necessary moisture, the sun can produce no effect and there can be no fresh vegetation. Thus, on Mars, the flow of water is the determining factor, and vegetation follows its course from the poles towards the equator. Observation shows that this is the case, and it has formed one of the strongest arguments in support of the idea of water conveyance by means of artificial canals. The opponents of the canal theory seem carefully to avoid any mention of this argument.