428 FOURTH REPORT — 1834. 



isting in the Milanese, with a view to their further extension. 

 The result was a project to join the Lake of Como with Milan 

 by means of the river Adda and the canal of Martesana. This 

 project was finally executed, and the difficulties of the naviga- 

 tion of the river Adda were overcome by means of a small cut 

 with ten locks in it, called the canal of Paderno, which was 

 finished in the year 1520. The next idea was to open a direct 

 communication between Milan and the Po, but this project, 

 with many others, such as the junction of the lakes of Como 

 and Maggiore with the Po. the Tecino with the Po near Pavia, 

 and the Adda near Cremona*, were postponed on account of 

 political circumstances. 



Hitherto the science of rivers had been greatly neglected, 

 and indeed had never made much progress until after the cele- 

 brated congress of scientific men in Tuscany in the year 1665. 

 This congress was appointed by the governments of Rome and 

 Florence with a view to put an end to the contests which had 

 taken place among the inhabitants bordering on the Val de 

 Chiana, (anciently called the Chesina Palus,) and now one of 

 the most fertile districts in Italy. It was precisely this river 

 which gave rise to the famous controversy in the Roman senate, 

 related by Tacitus, on the proposal for obviating the inundations 

 of the Tiber by diverting the Chiana into the Arno. The Chiana, 

 being situated between the Tiber and the Arno, had been alter- 

 nately forced backwards and forwards by the neighbouring popu- 

 lation until it had subsided into a noxious marsh, pouring out 

 its surplus waters wherever they could find a vent. The result 

 of the deliberation of the congress was a proposition by Cassini 



* " Memoria suUa Navigazione interna del Milanese," dell' Ingegnere Parea, 

 Annal., lib. i. 79. 



Almost the whole of the Val di Chiana has been raised by the process of 

 colmata, or warping, similarly to the practice adopted in the marshes border- 

 ing on the Humber in this country. 



It takes from five to six years to raise the surface as many feet. 



Torricelli alone recommended the system of Colmates in 1768. The Grand 

 Duke Leopold of Tuscany appointed a commission, at the head of which was 

 the learned Fossombroni, to direct the operations ; and on this occasion Fossom- 

 broni published a work, entitled, Memorie IdrauUco Sloriche sopra la Val di 

 Chiana, Firenze ] 769, in which the whole system is detailed. 



From experiments made on the depositions of the Ombrone (a small but 

 rapid river) at different periods, the deposits were found to be ^V; rr> 

 ■sV) -rr of tlie height of the water. It is to be wished that this system were 

 practised over the whole of the marshes of the Tuscan Maremma, which are 

 alone computed to amount to 300 square miles : the most considerable are the 

 marshes of Viareggio, Grosseto, Piombino and the Pontine mjirshes. The 

 works which were executed by Xinienes in the year 1767, in the marshes of 

 Grosseto, although magnificent and effective for a time, were afterwards ruined 

 by neglect : several attempts have since been made to renew them. 



