The white area at the top of this map is the south polar snow-cap, at about its usual maximum size. In some hard winters it attains a diameter of considerably over 100 degrees.
"The maximum area of the south polar snow-cap is usually more than 10,000,000 square miles instead of less than 2,500,000 as stated, but it is sometimes still greater during a hard winter. Then, where did the writer acquire the notion that the whole of the dark areas had to be covered with water? Only the canals and trenches have to be filled, and, at the highest computation, these would cover only 2,250,000 square miles! So even accepting her average of twenty feet depth of the snow (which would give about one foot of water over the whole area of the snow-cap), there would still be sufficient water to fill every canal and trench upon our planet to a depth of nearly four feet six inches.
"Let us suppose we have 700 series of canals, each averaging 1400 miles in length, and each series having an aggregate width (including the area of the irrigation trenches) of 21⁄4 miles. You will see that gives about 2,250,000 square miles to be covered with water. My estimate of the area to be covered is, however, much in excess of the real amount, as the average aggregate width of the series of canals would be less than I have assumed, and the trenches are shallow.
"I must also point out that only a small proportion of the whole number of canals would be in use at any given time, and the depth of the polar snows averages considerably more than twenty feet; so a very much greater depth of water can be secured in those canals which are in use. The main canals which are used for navigation purposes are, of course, much wider and deeper than the irrigation canals. In the hotter regions many covered compensation reservoirs are provided, and these make good the wastage caused by excessive evaporation where pipes cannot be used."
"Thank you, sir," I said; "the information you have now given me entirely confirms the figures as to the area of the snow-cap, &c., mentioned by Professor Lowell, but as regards the depth of the snow and the size of the area to be covered, he has with scientific caution refrained from estimating to the full extent which the facts you mention seem to warrant. In addition to this, no allowance has been made for the water derived from the northern snow-cap."
Thus vanished the theory which was supposed to support the view that the canals must be hopelessly unworkable, and could never be of any use for irrigation purposes.
It had also been argued that no intelligent beings would construct canals if the planet were generally flat, as it would only be necessary to let the water flow over the surface as far as it would go, and thus irrigate the parts reached by the water; whilst if it were not flat, the canals could not be constructed at all.
I asked Tellurio "What he thought of this suggestion?"
He replied, "Well, sir—here we have a planet believed to possess only a very scanty supply of water, which must require the most careful husbanding and economy in distribution; yet it seems to have been calmly suggested that we would deliberately waste the precious fluid by allowing it to flow at random over the small portion of our land which it would reach, where it might or might not be required! Our engineers, I may say, are quite capable of overcoming any difficulties arising from inequalities of the ground.