THE VAL DI CHIANA. 
423 
of increasing the rapidity of its current; the other, the gradual 
tilling up of the ponds and swamps, and raising of the lower 
grounds of the Yal di Chiana, by directing to convenient 
points the flow of the streams which pour down into it, and 
there confining their waters by temporary dams until the sedi¬ 
ment was deposited where it was needed. The economical 
result of these operations has been, that in 1835 an area of 
more than four hundred and fifty square miles of pond, marsh, 
and damp-sickly low grounds had been converted into fer¬ 
tile, healthy and well-drained soil, and, consequently, that so 
much territory has been added to the agricultural domain 
of Tuscany. 
But in our present view of the subject, the geographical 
revolution which has been accomplished is still more interest¬ 
ing. The climatic influence of the elevation and draining of 
the soil must have been considerable, though I do not know 
that an increase or a diminution of the mean temperature or 
precipitation in the valley has been established by meteoro¬ 
logical observation. There is, however, in the improvement 
of the sanitary condition of the Yal di Chiana, which was for¬ 
merly extremely unhealthy, satisfactory proof of a beneficial 
climatic change. The fevers, which not only decimated the 
population of the low grounds' but infested the adjacent hills, 
have ceased their ravages, and are now not more frequent than 
in other parts of Tuscany. The strictly topographical effect 
of the operations in question, besides the conversion of marsh 
into dry surface, has been the inversion of the inclination of 
the valley for a distance of thirty-five miles, so that this great 
plain which, within a comparatively short period, sloped and 
drained its waters to the south, now inclines and sends its 
drainage to the north. The reversal of the currents of the 
valley has added to the Arno a new tributary equal to the 
largest of its former affluents, and a most important circum¬ 
stance connected with this latter fact is, that the increase of 
the volume of its waters lias accelerated their velocity in a still 
greater proportion, and, instead of augmenting the danger from 
its inundations, has almost wholly obviated that source of 
