64 Proceedings of Philosophical Societies. [Jan", 



enough to compare the two methods ; and we have fannd theia 

 equally exact, and equally expeditious. 



^Thus, by uniling together the different memoirs which have 

 been communicated to him, along with the results of his own 

 svuvey, and the observations he made during his residence in the 

 Pontine Marshes ; as also with the levels, borings, and otlier 

 works, executed, at his desire, by that skilful engineer M. Scac- 

 cia, the author has been able to form, for his direction in the 

 project of draining these marshes, a collection of materials much 

 raore complete than those on which the former projects had been 

 imdertaken. The recent progress of the doctrines o^ running 

 ■water has also furnished hmi with means which were wanting ta 

 his predecessors. By the help of all these means, he has been 

 able to form a plan which will satisfy all the conditions required 

 by that celebrated problem, the draining of these marshes. 



The work is divided into four sections. The first contains 

 the description and dimensions of the Pontine basin \ the second 

 contains the state of these marslKs before the execution of the 

 wo.'ks ordered by Pius VI. In the third, there is given a 

 description of their present state, and an analysis of the difierent 

 projects formed anterior to 1811. The fourth and last contains 

 the author's own views, and his projects for the ulterior benefit 

 of the Pontine Marshes. In all of these we find a number of 

 curious and instructive tables, in which the author has collected 

 all the results of his observations and calculations. It is evident 

 that it is impossible for us to analyze them ; we shall only notice 

 the true measure of the uncient Koman foot, deduced from the 

 distance of the 42d and 4Gth milestone on the Appian way, the 

 only ones which have not been thrown down and removed. 

 The true Roman foot is 0-294246 metre, or 10 inches 10 lines 

 '044 of the old Paris foot. 



In the fourth section, which is the most extensive, and con- 

 tains more especially the application of the hydraulic theories, 

 the evil consequences of parinsr and burning the soil are shown; 

 also the present state of the Po, which, by means of the soil it 

 deposits at its mouth, now gains 70 metres yearly from the sea, 

 instead of 25, which it gained yearly from the 12th to the 17th 

 century ; the deposition of soil formed by the Tiber ; and lastly, 

 the contrary effect produced by the sea on the shore between 

 Anzo and Astura. " The Italians are, perhaps, the first who 

 gave to modern Europe the example of moderating the descent 

 and velocity of currents by means of falls, but they never 

 employed sluices for any other purpose ; the glory of using 

 hluices to estabhsh a communication between two large basins 

 was reserved for France. The canal of Briare, which joins the 

 Loire to the Seine, and which was finished in 1642, is the first 

 example of the union of two rivers by a canal traversing the 

 country lying between their two beds. This example was fol- 

 lowed with great success by the contrivers of the canal of 



