458 Alstrad Report of Agricultural Discussions. 



the assistancs of some pra,ctical men v/lio would imdertake to apply 

 gauges for measuring tlie quantity of water that fails on the land and 

 the quantity that passes thi-ough the di-ains on a given area. 



Sewage-water, then, is no doubt the most useful water for irrigation. 

 But here differences of oi>inion arc sometimes expressed. Some 

 maintain that a perfectly bright and clear sewage is best adapted for 

 irrigation. Others say that the muddier the sewage is, and the more 

 suspended matter it contains, the better. I contend that a moderately 

 clear sewage is the better, because that which contains much sus- 

 jjended matter is apt to produce on the sm-facc of the soil, especially 

 if not very porous, a silicious film, which dries and chokes up the 

 pores of the soil, and in this way does mischief. If the coarser 

 particles are skimmed off by the sewage being allowed to pass 

 through a grating, and the whole suspended matter finds its way into 

 the land, it v.-ill do good, if projicrly distributed. We need not be 

 particular in filtering the water to a nicety, but should be careful 

 not to allow too much of the suspended matter to flov/ * on the 

 land, especially if it is not a purely sandy porous soil, on which 

 sewage application is most efficacious. As a matter of cm-iosity, 

 I have brought with me a sample of the Maj)lin Sands, to which I am 

 inclined to think irrigation with sewage v\-ill be useful. It is supposed 

 that this sand contains some clay — not much, and also some other 

 fertilising matters. 



I now i)ass on to another description of water, next in point of 

 efficacy to sewage. Nile water conveys a vast amoimt of fertilising 

 matter to the natm-ally sterile plains on the banks of that river. Some 

 time ago I made an analysis of Nile v.ater, taken both at the rise of 

 the flood and when the flood was at its height. At the latter stage the 

 quantity of solid matter carried along is fom- times as great as at the 

 time when the Nile begins to rise, and it is chiefly in the deposit of 

 this solid matter that the fertilising action consists. Apart from this 

 deposit Nile water contains only 10 grains per gallon of solid matter 

 in solution, and perhaps the application of these muddy rivers can 

 hardly be called iiTigation proper; it is more the warping than the 

 irrigating of land. Suffice it, then, to say that muddy streams which 

 contain large quantities of suspended mineral, as well as organic 

 matter, are chiefly useful in depositing new soil. 



I pass on now to another description of water — that of waters which 

 have an equal temperature throughout the year. Water of that kind 

 is considerably warmer in winter than the atmosjihere of our fields. 

 We have some observations made upon this point by Mr. Whitley, of 

 Truro, in Cornwall ; also by Mr. liobert Smith, who has examined 

 several sj)rings in Exmoor, in Devonshire. Both these gentlemen are 

 of opinion that the temperature of irrigation-water dui-ing the spring 

 months is 10° higher than the temperatm-e of the air. Thus a 

 considerable quantity of heat is carried into our soils. Waters of a 

 Tmiform temperature generally come from deep sjn-ings; and deep 

 springs generally contain more mineral matter in solution. If water 

 passes through a thin layer of soil or rock, it has not much time to 

 dissolve the mineral matter. When it percolates through a large body 



