DISTRIBUTION. 59 



of 500 yards. Referring to a table giving the discharge of 

 gas per hour through pipes of various sizes, and remember 

 ing that the quantity delivered varies in proportion to the 

 square root of the inlet pressure, we get the following 

 values : 



For 2-inch diameter . . a = 4O-tenths. 



> 2 i > . a= II ,, 



3 > = 5 ft 



,,4,, . a= less than 2-tenths. 



To give a satisfactory supply, viz., + <r=2o, the initial 

 pressure must be 



With 2-inch diameter . . . . a + 6 + c = 6o 



2 2 Jl ^S 1 



3 ff .... ,, =25 



. 4 ft ' .... ,, =22 



Or suppose 2,000 cubic feet per hour is to be delivered 

 to a similar distance 



With a 4-inch diameter pipe . . a = 1 2-tenths 



,, 5-inch ,, ,, . . a = less than 2-tenths 



It should further be observed that a and b are inde- 

 pendent of the initial pressure. If the latter is insufficient, 

 c will suffer to a corresponding extent. 



Next let us note the effect of varying the rates of con- 

 sumption under a constant initial pressure, say from 1,000 

 cubic feet to 2,000 cubic feet and 25-tenths pressure. With 

 a 5-inch pipe the variation in the values of a would not be 

 noticeable, but with a 4-inch pipe we find 



With a consumption of 1 ,000 cub. ft. per hour, a = 2 and b + c = 23 

 ,, ,, 2,000 cub. ft. ,, a=i2 and b + c=i$ 



This example brings out the fact that for every size of 

 pipe there is a condition which we will call the carrying 

 limit. This will be reached in the example above quoted 



