2 6.2 Mr. mann’s 'freatife 
meafure of currents, as thofe of zendrini, himenii, 
Sec. 
Two other authors have lately wrote upon rivers 
and canals, but their works are not yet come to my 
hands; to wit, 
Father frisi, an Italian Barnabite, Profeffor of Mathe- 
matics at Milan, 
Mi de la lande, of the Royal Academy of Sciences 
at Paris, who has juft publifhed a Hiftorv in folio, with 
plates, of all the Navigable Canals in the World that 
have come to his Knowledge. 
Among the above authors, thofe marked with an 
afterilk (*) are they who have treated the fubjeft in 
queftion with the greateft exadtnefs or moft extent ; and 
it is from them chiefly that I fhall lay down fuch princi- 
ples and laws of aftion in rivers and canals as regard the 
fubjecft I have taken in hand. By this means I fhall 
avoid advancing any thing upon fo important a matter, 
but what is founded upon the moft certain and exaft ex- 
periments, and conformable to what are demon ftrated to 
he the real and unalterable laws of nature. 
SEC- 
