326 Modern Fishculture in Fresh and Salt Water. 



matter of wild guessing. An expert can guess with 

 some nearness by a mental estimate of how long it 

 would take a stream to fill a certain tank, but this is 

 only a guess. I had seen tables given in an algebraic 

 form, which, as far as I am concerned, might as well 

 never have been written, for, while as a schoolboy I 

 was forced through such studies, I promptly forgot 

 them. Anything mathematical was too heavy for a 

 brain not fitted to bear such burdens. Yet I must tell 

 in this book how to do the trick with exactness, and the 

 occasion brought the man, as usual. I wrote to a 

 friend, Mr. W. B. Osterhout, of Freeport, N. Y., one of 

 the engineers of the Brooklyn Water Works. He 

 writes : 



"Col. Fred M.^ther: It gives me great pleasure 

 to comply with your request of March 30. The for- 

 mula of which you speak is known as Francis' formula 

 and is for measuring the discharge of water over a 

 weir: Q=3.33XLXH? or Q=3.33XLxJtP: 0= 



Cubic feet of water per second ; L=Length of weir : 

 II=Head or depth of overflow. 



"The conditions are : The inner face of weir, as A B 

 ( Fig. 2 ) , must be not less than twice the depth of over- 

 flow, as A M measured from A to horizontal portion of 

 water's surface, A to M, and not to curved surfaces, at 

 C, and the length of A .A, of weir (Fig. i) not less 



