THE YAL DI CHI AN A. 
421 
and these obstructions, though not specifically intended for 
that purpose, naturally promoted the deposit of sediment and 
the elevation of the bed of the valley in their neighborhood. 
The effect of this measure and of the continued spontaneous 
action of the torrents was, that the northern slope, which in 
1551 had commenced at the distance of ten miles from the 
Arno, was found in 1605 to begin nearly thirty miles south of 
that river, and in 1645 it had been removed about six miles 
farther in the same direction.* 
In the seventeenth century, the Tuscan and Papal Govern¬ 
ments consulted Galileo, Torricelli, Castelli, Cassini, Viviani, 
and other distinguished philosophers and engineers, on the pos¬ 
sibility of reclaiming the valley by a regular artificial drainage. 
Most of these eminent physicists were of opinion that the 
measure was impracticable, though not altogether for the same 
reasons; hut they seem to have agreed in thinking that the 
opening of such channels, in either direction, as would give the 
current a flow sufficiently rapid to drain the lands properly, 
would dangerously augment the inundations of the river— 
whether the Tiber or the Arno—into which the waters should 
he turned. The general improvement of the valley was now 
for a long time abandoned, and the waters were allowed to 
spread and stagnate until carried off by partial drainage, infil¬ 
tration, and evaporation. Torricelli had contended that the 
slope of a large part of the valley was too small to allow it to 
be drained by ordinary methods, and that no practicable depth 
and width of canal would suffice for that purpose. It could 
be laid dry, he thought, only by converting its surface into an 
inclined plane, and he suggested that this might be accom¬ 
plished by controlling the flow of the numerous torrents which 
pour into it, so as to force them to deposit their sediment at 
the pleasure of the engineer, and, consequently, to elevate the 
level of the area over which it should he spread.f This plan 
* Mop.ozzo, Dello stato, etc., delVArno, ii, pp. 39, 40. 
t Torricelli thus expressed himself on this point: “ If we content our¬ 
selves with what nature has made practicable to human industry, we shall 
endeavor to control, as far as possible, the outlets of these streams, which, 
