50 



On Draining. 



no one month surpass the assumed point ? and that while these 

 elements of atmospheric agency were thus reduced on the one 

 hand, the fall of rain on the other, to be evaporated or dis- 

 charged, would have to be expressed bj perhaps half as much 

 again as the 27 inches, which is stated to be its exponent at 

 Bedford ? 



You have already recorded your conviction that such considera- 

 tions as these cannot be neglected with safety in regulating the 

 operations and improvements of agriculture ; and I cite your 

 words with pleasure, as lending authority and confirmation to my 

 own. 



" How can a fixed rule be laid down for the depth or the distance of 

 drains, or the size of pipes, when one county has 25 inches of rain and 

 another has 50 inches to be carried off by these drains ? The difference 

 is in fact more than this, for a large part of the downfall returns to the air 

 from the surface. According to the most recent and trustworthy experi- 

 ments published in this journal by Mr. Charnock, out of 331 inches of 

 rain no less than 25 inches are evaporated, 8^ inches only reach a depth 

 of 3 feet, and therefore pass through a drain. This was in Yorkshire ; 

 but at Kendal there fell 54 inches of rain. The evaporation there, how- 

 ever, would not be more, but less, because the air being moister must 

 dry what is exposed to it more slowiy, and the evaporation would not 

 exceed, probably fall short of, 21 inches. There remains, therefore, for 

 the drains 33 inches depth of water in this case, 8^ inches only in the 

 other — four times as much in Cumberland as in Yorkshire. Yet, hitherto, 

 if a man living in Oxfordshire said that inch pipes would drain his land 

 well, a voice from Ayrshire might exclaim, that it was absurd to use less 

 than 1^ inch pipe, which he found far the best. Yet the smaller pipe 

 might be more competent to do its duty in one place, than the larger one 

 in the other." 



" Henceforth, in speculations on the agriculture of the country we must 

 never lose sight of our material variations in climate." — vol. xi. p. 394. 



But I hope that by this time I shall have succeeded in carry- 

 ing conviction upon the point also into the mind of the most 

 determined sceptics, if any such there be. 



Now let us recur to our exposition of the specific case which 

 led us into this investigation. If, as Mr. Parkes, and other 

 authorities say, the contraction and opening of stiff clays by the 

 action of atmospheric heat is necessary to the efficiency of deep 

 drainage in such soils, and if, as I think we have demonstrated, 

 and as, indeed, in these parts we know by experience, such pro- 

 cess cannot be reckoned upon in ordinary years, and indeed can 

 scarcely be said to occur, effectually, more than once in a quarter 

 of a century, it seems indispensable to devise some system which 

 may serve to secure the benefits of deep drainage without 

 its help. Now the surface-soil, and generally the upper por- 

 tion of the ground to a certain depth, is more or less friable 

 and pervious, and could be easily relieved of its water long before 

 this could under any circumstances filter through its bed of clay. 



