36 The Theory of Irrigation. [January, 



rivers, polluting their waters and destroying their fish. The 

 advisability of adopting a system of irrigation in England has, 

 however, of late years, become a necessity, and one which 

 must annually increase in urgency, entirely irrespective of 

 the subject of sewage utilisation ; and it is only by a proper 

 appreciation of this fact, and of the causes to which it is 

 due, that we can expect the subject will receive attention. 

 In order to convey the full meaning of the foregoing remarks, 

 it is necessary that we should consider, somewhat in detail, 

 the true theory of irrigation, which will be found, as we 

 proceed, to owe its origin to a disturbance, by the works of 

 man, of the balance originally prescribed by nature between 

 evaporation and precipitation. 



A careful study of the works of nature, in their primitive 

 state, cannot fail to show the beautiful harmony of creation, 

 and the perfect economy of its arrangements whilst con- 

 tributing only to the support of brute creation. To man, 

 however, in his more elevated sphere, has apparently been 

 given a certain power over the elements, by means of which 

 he can disturb that harmony of existence, which not 

 only is not violated, but is actually promoted by the lower 

 orders of creation. The student of history, by applying 

 this test in his researches into the records of past ages, will 

 find that to man alone may be attributed such a disturbance 

 of the balance of forces as, in progress of time, has led to 

 serious convulsions of nature, affecting not only the geography 

 of the earth, but also many atmospheric and climatic changes 

 in different parts of the world, the occurrence of which there 

 can be no difficulty in establishing. " If* we compare the 

 physical condition of certain ancient countries at the present 

 day with the descriptions given by old historians and geo- 

 graphers, of their fertility and general capability of minis- 

 tering to human uses, it will be found that more than one- 

 half of their whole extent — including the provinces most 

 celebrated for the profusion and variety of their spontaneous 

 and their cultivated products, and for the wealth and social 

 advancement of their inhabitants — is either deserted by 

 civilised man and surrendered to hopeless desolation, or 

 at least greatly reduced in both productiveness and popu- 

 lation/' 



There are two great primary causes which, above all others, 

 may be said to have led to these remarkable changes ; and 

 these are, first, the destruction of forests; and, secondly, 

 surface and subsoil drainage. We shall consider briefly 

 these two subjects in the order in which they are mentioned 



* " Man and Nature," by George P. Marsh ; 1864, p. 3. 



