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DISTRIBUTION OF GAS THROUGH MAINS. 



Quantities delivered by an eighteen-inch Main in cubic feet. 



In the foregoing Tables I have considered the mains as horizontal. The 

 quantities of gas noted as passing through them are in many instances 

 checked by experiment, and may be safely relied on in practice. Inequalities 

 of interior surface will affect the passage of the gas through the pipes ; but 

 as those inequalities constantly vary, no rules can be given by which to ascer- 

 tain the amount. The quantities given for the discharge through pipes above 

 six inches in diameter are too small, according to the French mathematicians, 

 and strictly they are so. The question is yet to be answered, What influence 

 does the diminution of surface in a large pipe exert over the discharge? 

 Some years ago I calculated the size of a pipe according to the data given 

 by them, and I found it necessary to increase the pressure three-tenths of 

 an inch beyond the calculated pressure, to produce the desired effect. A 

 four-inch pipe six miles long will discharge 852 cubic feet of gas with a press- 

 ure of three inches ; an eight-inch pipe will certainly discharge more than 

 four times that quantity under the same circumstances, but there is no cor- 

 rect data from which the extra discharge can be calculated. This being the 

 case, the prudence of constructing the tables for pipes beyond the diameter 

 of six inches will be questioned; but to this charge I plead " not guilty," 



