LECTURES AND ESSAYS READ AT INSTITUTES. 277 



Since a line of tile cannot be placed under pressure of a head except when 



the soil is saturated, the necessity of having every inch of the tile so laid that 



the water will run off becomes apparent. Thus in fig. 7 A. D. E. B. repre- 



^^^^^^^E^:^^^,^^^ sent a line of badly laid tile, the true 



^ — ^^^ ^^^^^^^^ ^ grade being from A. to B. Such a drain 



aN^"^"^ -^^^ may work quite well when the ground is 



Section Tile Drain. Fig 7. full of water, the pressure above carrying 



the current through the depression ; buc as the ground grows dry the current 

 becomes less strong; sand or silt is deposited in the depression, and in time, 

 be it longer or shorter, the tile will surely be filled to the grade line A. B. 



I had some experience with a drain of exactly that nature ; it was built of 

 three-inch tile through a very wet place, in 1874, and in 1880 it had become 

 completely choked. Digging down, we found the tile as shown by the crook 

 A, D, E, B. There is no doubt that the tiles had always been as we found 

 them, yet the drains worked efficiently, or at least kept the water down, for 

 six years; but when we opened them, the sand was packed firmly clear to the 

 grade line, filling eight tiles completely full. This may explain why drains that 

 often give good satisfaction for several years, finally clog up and fail. Noth- 

 ing is more permanent than a tile drain properly laid. [I will except peat soil 

 from the above statement, as that frequently settles when the water is drawn 

 off, carrying the tile with it]. When such an event happens with a line of 

 tile laid by a farmer, he is likely to ascribe the failure to the tile, and is ready 

 to condemn the tile furnished by a certain manufacturer, or else the whole 

 system of tile drainage. 



Besides the ability of the tile to carry off water, we must know the amount 

 of water to be carried off before we can. determine the capacity of given sized 

 drains. The water comes principally from the rainfall — all primarily from 

 that — but we will put it from rainfall and springs. No rules can be laid 

 down for the size of pipes that will drain springs; each case would have to be 

 taken by itself. The rain fall in this part of our country is to be taken into 

 consideration ; its amount is about 30 inches per year. That amount would 

 be, for 100 days, only three-tenths of an inch per day, and at first glance it 

 might seem that if the drains were large enough to remove from each acre 

 that amount, they would answer very nicely. A study of the meteorological 

 records, however, gives one a different opinion. Then it is seen that about 

 50 per cent of our rain, falls in heavy showers, amounting to an inch in 34 

 hours. During each year we have three or four showers that bring from two 

 to three inches of rain within 24 hours. The soil itself is a great retainer of 

 this moisture, dry sand holding 25 per cent, loamy soil 40 per cent, clay loam 

 50 per cent, and pure clay 70 per cent of its weight, that cannot be drained 

 off. If the soil was already very wet a greater proportion of a rain would pass 

 into the tiles, than if dry. 



Experiments made with a Lysimeter by Lawes and Gilbert, of England, 

 showed that the drainage in summer varied from 7.9 per cent to 47.6 

 per cent of the rain fall; and in winter from 39.8 per cent to 80.1 per cent. 

 Drains at a depth of 20 inches carried away 44. G per cent of the rainfall, at 

 a depth of 40 inches 47.4 per cent, and at a depth of GO inches 42.1 per cent. 

 Dr. Sturtevant, at Boston, found the percentage of the drainage water to rain- 

 fall at a depth of three feet to be as follows, for the years 1876, 1877, 1878, 

 and 1879 : 



