42 The Theory of Irrigation . [January, 



between the constituents of the manure and the soil, it is 

 also further required before that soil will yield up the proper- 

 ties thus obtained for the purposes of vegetation. 



Having now considered in what manner irrigation, has 

 been rendered a necessary adjunct to cultivation, it remains 

 but to state briefly what steps are required for the con- 

 servancy of rainfall in order to render it most conducive 

 towards a restoration of that balance in nature which 

 previous operations of man have tended so seriously to 

 disturb. These are two ; namely, the prevention of waste 

 by storeage, and the construction of channels for the proper 

 distribution of water so collected, properly fitted with 

 mechanical appliances for the regulation of the supply to 

 different fields or districts as it may be required. 



It is not the object of the present paper to enter into any 

 account of the works or contrivances necessary for the 

 collection and distribution of rainfall and drainage water; 

 some brief allusion to what has been done in this respect, in 

 former ages and in other countries, has already been made 

 in the pages of this journal, but a complete study of the 

 history and engineering nature of such works would occupy 

 more space, and deserve more attention, than could be given 

 to the subject in the concluding part of an article which has 

 already occupied so much space ; it may, however, be con- 

 sidered of sufficient importance to form the theme for a 

 separate article upon some future occasion. In conclusion, 

 it may be remarked that the question of sewage irrigation is 

 one entirely distinct from that of simple irrigation by means 

 of water alone ; the purposes of the one being but the 

 application of moisture to the soil, it in no way supersedes 

 the necessity for manuring, whilst the former combines the 

 application of manure together with irrigation. It does not 

 seem at all probable that the two systems will ever be 

 carried out in conjunction with each other, neither is it 

 necessary that they should be combined. It is also clear 

 that, whereas sewage irrigation is only practicable to a certain 

 limited extent, and in localities bordering upon towns or 

 places where a number of human habitations are congre- 

 gated together, irrigation in its simple form may be adopted, 

 to a greater or less extent, wherever land is brought under 

 cultivation. 



