358 CLIMATIC AND GEOGRAPHICAL EFFECTS OF AQUEDUCTS. 
Climatic Effects of Draining Lakes and Marshes. 
The draining of lakes, marshes, and other superficial accu¬ 
mulations of moisture, reduces the water surface of a country, 
and, of course, the evaporation from it. Lakes, too, in elevated 
positions, lose a part of their water by infiltration, and thereby 
supply other lakes, springs, and rivulets at lower levels. Hence, 
it is evident that the draining of such waters, if carried on 
upon a large scale, must affect both the humidity and the tem¬ 
perature of the atmosphere, and the permanent supply of 
w r ater for extensive districts.* 
Geographical and Climatic Effects of Aqueducts , Reservoirs, 
and Canals. 
Many processes of internal improvement, such as aque¬ 
ducts for the supply of great cities, railroad cuts and embank¬ 
ments, and the like, divert water from its natural channels, 
and affect its distribution and ultimate discharge. The col¬ 
lecting of the waters of a considerable district into reservoirs, 
to be thence carried off by means of aqueducts, as, for ex¬ 
ample, in the forest of Belgrade, near Constantinople, deprives 
the grounds originally watered by the springs and rivulets of 
the necessary moisture, and reduces them to barrenness. Sim¬ 
ilar effects must have followed from the construction of the 
numerous aqueducts which supplied ancient .Rome with such 
a profuse abundance of water. On the other hand, the filtra¬ 
tion of water through the banks or walls of an aqueduct car- 
* In a note on a former page of this volume I noticed an observation 
of Jacini, to the effect that the great Italian lakes discharge themselves 
partly by infiltration beneath the hills which bound them. The amount 
of such infiltration must depend much upon the hydrostatic pressure on 
the walls of the lake basins, and, of course, the lowering of the surface of 
these lakes, by diminishing that pressure, would diminish also the infil¬ 
tration. It is now proposed to lower the level of the Lake of Como some 
feet by deepening its outlet. It is possible that the effect of this may 
manifest itself in a diminution of the water in springs and fontanili or 
artesian wells in Lombardy. 
