The reply that has been made to this is twofold.

In the first place, it should be remembered that the theory, as Mr.Lowell presents it, does not assert that the visible lines are the actual canals, but only that they are strips of territory intersected, like Holland or the center of the plain of Lombardy, by innumerable irrigation canals and ditches.

To construct such works is clearly not an impossible undertaking, although it does imply great industry and concentration of effort.
In the second place, since the force of gravity on Mars is in the ratio of only 38 to 100 compared with the earth's, it is evident that the diminished weight of all bodies to be handled would give the inhabitants of Mars an advantage over those of the earth in the performance of manual labor, provided that they possess physical strength and activity as great as ours.

But, in consequence of this very fact of the slighter force of gravity, a man upon Mars could attain a much greater size, and consequently much greater muscular strength, than his fellows upon the earth possess without being oppressed by his own weight.

In other words, as far as the force of gravity may be considered as the decisive factor, Mars could be inhabited by giants fifteen feet tall, who would be relatively just as active, and just as little impeded in their movements by the weight of their bodies, as a six-footer is upon the earth.