LONGITUDLN-AL DIKES. 493 



For these reasons, many experienced engineers are of opinion 

 that tlie system of longitudinal dikes is fundamentally wrong and 

 it has been argued that if the Po, the Adige and the Brenta had 

 been left unconfined, as the Nile formerly was, arid allowed to 

 spread their muddy waters at will, according to the laws of na- 

 ture, the sediment they have carried to the coast would have been 

 chiefly distributed over the plains of Lombardy. Their banks, it 

 is supposed, would have risen as fast as their beds, the coast-line 

 would not have been extended so far into the Adriatic, and, the 

 current of the streams being consequently shorter, the inclination 

 of their channel and the rapidity of their flow would not have 

 been so greatly diminished. Had man, too, spared a reasonable 

 proportion of the forests of the Alps, and not attempted to con- 

 trol the natural drainage of the surface, the Po, it has been said, 

 .would resemble the Nile in all its essential characteristics, and, 

 in spite of the difEerence of climate, perhaps be regarded as the 

 friend and ally, not the enemy and the invader, of the population 

 which dwells upon its banks. 



But it has been shown by Humphreys and Abbot that the sys- 

 tem of longitudinal dikes is the only one susceptible of advan- 

 tageous apphcation to the Mississippi, and if we knew the primi- 

 tive geography and hydrography of the basin of the Po as well 

 as we do those of the valley of the great American river, we 

 should very probably find that the condemnation of the plan 

 pursued by the ancient inhabitants of Lombardy is a too hasty 

 generalization, and that the case of the Nile is an exception, 

 not an example, of the normal regime and condition of a great 

 river.* 



no less than 80,000 square miles. Its current was computed as having a width ' 

 of from thirty to forty miles. A large population was for months dependent 

 for its daily food on rations distributed by the National Government. 



* Embankments have been employed on the lower course of the Po for at 

 least two thousand years, and for some centuries they have been connected in 

 a continuous chain from the sea to the vicinity of Cremona. From early ages 

 the Italian hydrographers have stood in the front rank of their profession, and 

 the Italian literature of this branch of material improvement is exceedingly 

 voluminous, exhaustive and complete. 



" The science of rivers after the barbarous ages," says Mengotti, " may be 

 said to have been bom and perfected in Italy." The eminent Italian engineer, 

 Lombardini, published in 1870, under the title of Quida alio studio dell' idrolo- 



