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deductions from the most carefully constructed formulfe. The shape of the 

 river bed, curyes in the stream, the length of the course, when it has free action 

 uninfluenced by rapids, &c., must all be disturbing elements to be taken into 

 account in each instance. I am informed, however, by Mr. Curley that the 

 tables at the end of Neville's Hydraulics may be relied upon as sufficiently 

 accurate. According to these by making a section of the river bed, and knowing 

 the mean hydraulic depth and inclination, the velocity can be determined at any 

 state of the flood, and hence, of coiu-se, the discharge. Now amongst these data 

 the only variable one is the hydraulic mean depth, and on this depends the observed 

 height ; the problem is readUy solved this last being determined. It might be, 

 however, very desirable in aay case to check this result by ascertaining the 

 velocity of the current directly in the following way : — 



A section of the bed must be made at some place where there is a straight 

 reach of the river unincumbered with rocks and other inequalities. This can be 

 done by taking soundings at equal intervals, whence the area of the section can 

 be easily ascertained ; a gauge then erected in this spot and divided into feet 

 and decimals of feet enables us to note the height of the flood at any time, and 

 a space of 100 ft. measured along the bank enables us to determine the rate of 

 the stream by any floating substance thrown into it ; the number of seconds it 

 takes to pass between the two marks giving its velocity. Hence (by Table VII. 

 in Neville's Hydraulics) can be found its mean velocity, which if reduced to feet 

 per minute multiplied into the area of the section in square feet, gives the 

 volume of water in cubic feet per niimute. 



The experiments which I have been making on the Onny, a small stream 

 ■which flows near my house, have not been carried out long enough to afford any 

 very decided or important results, but from what they indicate so far, I have 

 every confidence that if they are continued during the course of a few years 

 they will well repay the trouble. Since the commencement of these obser- 

 vations there have been four considerable floods — on the 20th of December, the 

 6th and 31st January, and the 12th of February. In these cases it would appear 

 that the greatest deposit occurred towards the commencement of the rainfall, a 

 result which we might easily anticipate, as it is in the first flushing of the 

 channel that the previously deposited mud would be stirred up and carried 

 down. Every little rivulet, as it svibsides after a flood, leaves a contingent of 

 finely levigated mud, ready for the next down-potir to carry into the river, 

 and when this supply is exhausted the ratio of the sediment must also neces- 

 sarily fall off. On the 31st of January the discharge of water was 34,500 cubic 

 feet, and of sediment (dry) 610 lbs. per minute. 



It will be seen by reference to the register that the proportion of this 

 sediment varies from about zero to 26 grains in the 100 ounces of water. This 

 latter large result was obtained after the sudden and violent rain of the 5th of 

 January, which, however, was a very local storm, as it appears from the 

 register that the rainfall on the aide of the Longmynd on that day, at Wool- 

 itaatoB, was only '09. 



