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See in Lombardini, Sulle Inondazioni in Francia, p. 87, notices of the action of currents transporting only fine material in wearing down hard rock. In the sluices for gold-washing in California having a grade of 1 to 14 1/2, and paved with the hardest stones, the wear of the bottom is at the rate of two inches in three months.
The tenacity with which the parched soil of Egypt retains the supply of moisture it receives from the Nile is well illustrated by observations of Girard cited by Lombardini from the Memoires de l'Academie des Sciences, t. ii., 1817.
The level of certain parts of the bed of the river referred to by Lombardini as constant, is not their elevation as compared with points nearer the sea, but relatively to the adjacent plains, and there is every reason to believe that the depression of the Adriatic coast, whether, as is conceivable, occasioned by the mere weight of the fluviatile deposits or by more general geological causes, has increased the slope of the bed of the river between the points in question and the sea.
Finding out, after an expenditure of several thousand dollars, the defect, he got a new claim from the late President Lombardini of thirty miles square, which he will probably now pin tight in Sonora. The defect of our two last treaties with Mexico was in not having a clause inserted reducing all titles to land to six miles square, as a consideration for the enhanced value by the annexation.
His letter to his pupil, Signora Maddelena Lombardini, contains invaluable advice on violin practice and study, especially on the use of the bow, and his treatise on the acoustic phenomenon known as "the third sound," together with his work on musical embellishments, may at any time be read with profit.
And in like wise, the trees which be planted along the mountains do much deaden the violence of the waters that flow from them." Lombardini attaches great importance to the planting of rows of trees transversely to the current on grounds subject to overflow. Removal of Obstructions.
"There are huge pyramids of mountains now bare and bleak from base to summit, which men still living and still young remember seeing richly mantled with all but primeval forests." The clearing of the mountain valleys of the provinces of Bergamo and of Bescia is recent, and Lombardini informs us the felling of the woods in the Valtelline commenced little more than forty years ago.
Lombardini lays down the following general statement of the effects of river embankments: "The immediate effect of embanking a river is generally an increase in the height of its floods, but, at the same time, a depression of its bed, by reason of the increased force, and consequently excavating action, of the current.
The Po is not continuously embanked except for the lower half of its course. See Lombardini, Dei cangiamenti nella condizione del Po, p. 29. All the sediment carried into the lakes by their tributaries is deposited in them, and the water which flows out of them is perfectly limpid.
The floods of the affluents of the Tiber form an exception to this law, being generally coincident, and this is one of the explanations of the frequency of destructive inundations in that river. Lombardini, Guida allo Studio dell' Idrologia, ff. 68; same author, Esame degli studi sul Tevere.
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