276 



STATE BOARD OF AGRICULTURE. 



Association that a philosopher in Ohio had found that the size of tiles should 

 decrease as we near the outlet. His method of reasoning was doubtless as 

 follows : for instance, he has noticed that if a long line of six-inch tile be 

 simply filled at the upper end, in a short distance it is not filled, and if it is 

 long enough and not receiving water throughout its length, the stream becomes 

 less and less, and finally could be contained in a five-inch, and then in a four- 

 inch, and then in a three-inch tile. If a mile long its discharge is only seven 

 per cent of what would pass through the first tile under the same head, and the 

 remedy proposed was to make the tile decrease in size just as fast as the stream 

 decreased, so as to have every tile full. 



Had he considered that the true cause of the decrease of the stream was 

 friction, and that could this be entirely eliminated there would be no decrease, 

 his reasoning would have brought a different result. The friction is more in 

 small tile, in proportion to capacity, than in large tile, and the change pro- 

 posed would simply add obstructions to those already existing in the pipe. 

 While it is impossible to make a long line of tile run full at the outlet without 

 some considerable head, because of this friction, still the aim should be rather 

 to construct the drain so as to discharge what passes through the first tile than 

 to make the outlet tile run full. To do even this will require tiles which con- 

 tinually increase as the outlet is approached. 



The following table shows the effect of increasing the length of a pipe. If 

 the discharge through a pipe one foot long be called 1,000, the discharge through 

 a pipe one mile long would be shown by the following table : 



The amount discharged is seen, by above table, to vary from three per cent 

 with the one inch pipe, to 13 per cent nearly with the 18 inch pipe. The 

 friction holds back in the first case 9? per cent of the water received, and in 

 the latter case 88 per cent. The formula for the flow of water through pipes is 

 obtained by comparing with the actual flow, the one most commonly used and 

 giving results very close to the observed ones; the velocity in feet per second 

 equals 50 times the square root of the diameter, multiplied by the head and 



divided by the length plus 50 diameters, as follows: y=50 ^ — — — , in which 



I + 50d 

 y=velocity; (?=diameter; «^total head or fall; Z=Iength. The volume is 

 found by multiplying the area of the stream issuing by the velocity. This 

 formula is seen to approximately vary inversely as the square root of the length. 

 The velocity of water is not sensibly affected by the nature of the pipe, pro- 

 vided it is smooth. 



