f water such great distances would be by a system of
water-tight and air-tight tubes laid _under the ground._ The mere
attempt to use open canals for such a purpose shows complete ignorance
and stupidity in these alleged very superior beings; while it is certain
that, long before half of them were completed their failure to be of any
use would have led any rational beings to cease constructing them.

He also fails to consider the difficulty, that, if these canals are
necessary for existence in Mars, how did the inhabitants ever reach a
sufficiently large population with surplus food and leisure enabling
them to rise from the low condition of savages to one of civilisation,
and ultimately to scientific knowledge? Here again is a dilemma which is
hard to overcome. Only a _dense_ population with _ample_ means of
subsistence could possibly have constructed such gigantic works; but,
given these two conditions, no adequate motive existed for the
conception and execution of them--even if they were likely to be of any
use, which I have shown they could not be.

_Further Considerations on the Climate of Mars._

Recurring now to the question of climate, which is all-important, Mr.
Lowell never even discusses the essential point--the temperature that
must _necessarily_ result from an atmospheric envelope one-twelfth (or
at most one-seventh) the density of our own; in either case
corresponding to an altitude far greater than that of our highest
mountains.[17] Surely this phenomenon, everywhere manifested on the
earth even under the equator, of a regular decrease of temperature with
altitude, the only cause of which is a less dense atmosphere, should
have been fairly grappled with, and some attempt made to show why it
should not apply to Mars, except the weak remark that on a level surface
it will not have the same effect as on exposed mountain heights. But it
_does_ have the same effect, or very nearly so, on our lofty plateaux
often hundreds of miles in extent, in proportion to their altitude.
Quito, at 9350 ft. above the sea, has a mean temperature of about 57 deg.
F., giving a lowering of 23 deg. from that of Manaos at the mouth of the Rio
Negro. This is about a degree for each 400 feet, while the general fall
for isolated mountains is about one degree in 340 feet according to
Humboldt, who notes the above difference between the rate of cooling for
altitude of the plains--or more usually sheltered valleys in which the
towns ar