UEPORT ON HYDRAULICS. — PART II. 



431 



through in one second, by a body floating on the surface of a 

 river, divided by the same parameter, will give the height due to 

 the velocity of the surface, which, added to the height of the 

 river, will give the whole effective or equivalent height : the 

 square root of the product of the equivalent height by the para- 

 meter will give the velocity at the bottom of the section. 



Two thirds of the product of the velocity at the bottom by 

 the whole equivalent height, minus two- thirds of the product of 

 the velocity at the surface by the height added to the actual 

 height, will give the mean velocity. 



Finally, the product of the mean velocity by the actual breadth 

 and the actual height will give the quantity of water that passes 

 in one second through the rectangular section. 



Zendrini's observations on the continual rise of the Adriatic 

 Sea, in confirmation of the opinions of Sabbadini, Montanari, and 

 Manfredi, and on the prolongation of the whole shore of the Po, 

 as far as Ancona, and his Report on the diversion of the Ronco 

 and Montone, rivers near Ravenna, together with the extension 

 of the sandbanks at the mouths of the different rivers, are 

 extremely interesting. 



His great experience on this subject led him to conclude that 

 a harbour ought not to have a turbid river either on its right or 

 left side within a distance of seven or eight miles. 



As early as the commencement of the eleventh century the 

 opinions of philosophers coincided very nearly with the theory 

 that the surface of the Adriatic Sea was continually rising, and 

 certain indications along its shores seemed to confirm the cor- 

 rectness of these opinions. The cause was generally attributed to 

 the continual accumulation of the substances brought down by 

 the rivers and collected on the beach, and which, by prolonging 

 the shores and contracting the outline, caused an elevation of 

 the surface of the sea. This explanation, says Paul Frisi, would 

 be very plausible if the Baltic did not exhibit at one and the 

 same time an enlargement of its shores and a depression of its 

 superficial level ; and if it were not evident that as all seas must 

 have a common level with respect to each other, the absolute 

 height of the waters cannot be raised in one without being at the 

 same time elevated in all the rest. In the Memoirs of the 

 Academy of Stockholm, Celsius, Dalin, Stembeek, and others 

 have given a long statement of facts, which prove very clearly 

 the extension of all the shores of the Baltic Sea*. But what- 



• See Mr. Lyell's Geology relative to the Delta of the Po, vol. i. pp. 236, 237 ; 

 also a paper recently presented by that gentleman to the Royal Society on the 

 rise of the shores of the Baltic Sea. The following examples in illustration of 

 Manfredi's theory are mentioned by Col. Leake : Ilafonisi, an island formerly 



