IN THE MONTH OF FEBKUARV 1852. 147 



"Multiply 2,500 times the diameter of the pipe in feet by 

 the height in feet, and divide the product by the length in 

 feet, added to 50 times the diameter, — then the square root 

 of the quotient will be the velocity of discharge in feet per 

 second." 



This rule is a tolerably safe one in practice. I believe it 

 to be under the truth for large pipes and high velocities; and 

 it requires to be used with judgment in determining the dis- 

 charge by small pipes, where the system is complex. 



The circumstances under which the water was discharged 

 from the Rhodes Wood Reservoir were so far complicated as 

 to render the determination of the proper co-efficient a ques- 

 tion of some difficulty. 



Two pipes, each 4 feet in diameter, and 303 and 370 feet 

 respectively in length, were diminished at the outer end to 

 3 feet, the vvater being finally passed through a pipe of that 

 diameter for about 20 feet in length, and through a 3-feet 

 valve, divided into two compartments. One pipe branched 

 into two at the end, having a valve at each branch, and 

 through both of which water was discharged. The pipe is 

 too large and the circumstances too complex to admit of the 

 application of the rule for calculating the discharge through 

 pipes. The water would approach the opening with consi- 

 derable velocit}', acquired in its passage through the 4-feet 

 pipe, and therefore, rather a higher co-efficient than that 

 usually employed for finding the velocity through openings, 

 should be adopted. From a consideration of all these cir- 

 cumstances, and from other observations upon the actual 

 quantity of water discharged, the co-efficient adopted was 

 5.5 ; and this may be rather lower than it ought to be. 



With this co-efficient, however, the calculations came out, 

 as will be shortly shewn. 



The month of January had been marked by a considerable 

 fall of rain, and at the end of the month the ground was 

 thoroughly saturated, the streams and springs yielding con- 



