R I V 



8. Eytelwein, a German mathematician, gives the following- formula 

 for the mean velocity of the stream of a canal. Let v be the mean velo- 

 city of the current in English feet, a the area of the vertical section of 

 the stream, p the perimeter of the section, or sum of the bottom and two 

 sides, I the length of the bed of the canal corresponding to the fall h t all 

 in feet ; then 



i - 0.109 + J 



9582 .- 4. 0.0111 



9. To find experimentally the velocity of the water in a river, and the 

 quantity which flows down in a given time, observe a place where the 

 banks of the river are steep and nearly parallel, and by taking the depth 

 at various places in crossing make a true section of the river. Stretch a 

 string at right /'s. over it, and at a small distance another parallel to 

 the first. Then take an apple, orange, or a pint or quart bottle partly 

 filled with water so as just to swim in it, and throw it into the water 

 above the strings. Observe when it comes under the first string by 

 means of a quarter second pendulum or a stop watch, and observe also 

 when it arrives at the second string. By this means the velocity of the 

 tipper surface, which in practice may frequently be taken for that of the 

 whole, will be obtained. The section of the river at the second string 1 

 must then be ascertained by taking various depths as before, and the 

 mean of the two will be obtained by adding both together and taking 

 half the sum for the mean section. Then the area of the mean section 

 in square feet being multiplied by the distance between the stringif in 

 feet will give the contents of the water in solid feet which passed from 



