REPORT ON HYDRAULICS. PART 11. 



4^ 



diminution of ^^th of the superficial velocity for each metre in 

 depth, so that v being the velocity, d the required depth, the 

 mean velocity of the particles will be f (1 — 0*0125 d). 



But the experiments of Brunnings do not authorize such a 

 conclusion. 



The tachometer of Woltmann, published in the year 1790, was 

 constructed upon the principle of the common windmill, and 

 consisted of four small vanes, attached to an axle and connected 

 with wheel-work : the instrument, being exposed to the direct 

 action of the current at different depths, indicated by the number 

 of its revolutions the velocity of the stream. 



The following Table gives the result of some of the experi- 

 ments made by Funk (amongst others on the Elbe and Weser,) 

 on the superficial and mean velocities of different parts of the 

 same section of the river contrasted with the experiments of 

 Dubuat. 



The following experiments, by Brunnings, on the velocities of 

 the Rhine, Elbe, and Weser, were also made by Woltmann's 

 machine. 



It is somewhat remarkable, that the Nouvelle Architecture of 

 M. Prony, published in 1790, contains nothing relative to rivers. 



