578 



SCIENCE. 



[N. S. Vol. XXII. No. 567. 



branches of engineering, I could do no 

 more than repeat a number of platitudes, 

 which you know at least as well as I do. 

 You would probably have fallen asleep 

 before I was half finished, and it would be 

 the best thing- you could do. I think, then, 

 that it will be better to select one branch, 

 a branch on which comparatively little has 

 been written, which has, I understand, a 

 special interest for South Africa, and which 

 has occupied the best years of my life in 

 India, southern Europe, central Asia and 

 Egypt — I mean the science of irrigation. 

 My subject is water— living, life-giving 

 water. It can surely never be a dry sub- 

 ject; but we all know that with the best 

 text to preach on the preacher may be as 

 dry as dust. 



. IRRIGATION: WHAT IT MEANS. 



Irrigation may be defined as the artificial 

 application of water to land for the pur- 

 poses of agriculture. It is, then, precisely 

 the opposite of drainage, which is the arti- 

 ficial removal of water from lands which 

 have become saturated, to the detriment of 

 agriculture. A drain, like a river, goes on 

 increasing as affluents join it. An irriga- 

 tion channel goes on diminishing as water 

 is drawn off it. Later on I shall show you 

 how good irrigation should always be ac- 

 companied by drainage. 



In lands where there is abundant rain- 

 fall, and where it falls at the right season 

 of the year for the crop which it is intended 

 to raise, there is evidently no need of irri- 

 gation. But it often happens that the soil 

 and the climate are adapted for the culti- 

 vation of a more valuable crop than that 

 which is actually raised, because the rain 

 does not fall just when it is wanted, and 

 there we must take to artificial measures. 



In other lands there is so little rain that 

 it is practically valueless for agriculture, 

 and there are but two alternatives — irriga- 

 tion or desert. It is in countries like these 



that irrigation has its highest triumph ; nor 

 are such lands always to be pitied or de- 

 spised. The rainfall in Cairo is on an 

 average 1.4 inch per annum, yet lands 

 purely agricultural are sold in the neigh- 

 borhood as high as £150 an acre. 



This denotes a fertility perhaps un- 

 equaled in the case of any cultivation de- 

 pending on rain alone, and this in spite of 

 the fact that the Egyptian cultivator is in 

 many respects very backward. The ex- 

 planation is not far to seek. All rivers in 

 flood carry along much more than water. 

 Some carry alluvial matter. Some carry 

 fine sand. Generally the deposit is a mix- 

 ture of the two. I have never heard of 

 any river that approached the Nile in the 

 fertilizing nature of the matter borne on 

 its annual floods ; with the result that the 

 plains of Egypt have gone on through all 

 ages, with the very minimum of help from 

 foreign manures, yielding magnificent crops 

 and never losing their fertility. Other 

 rivers bring down little but barren sand, 

 and any means of keeping it off the fields 

 should be employed. 



PRIMITIVE MEANS OF IRRIGATION. 



The earliest and simplest form of irriga- 

 tion is effected by raising water from a 

 lake, river or well, and pouring it over the 

 land. The water may be raised by any 

 mechanical power, from the brawny arms 

 of the peasant to the newest pattern of 

 pump. The earliest Egyptian sculptures 

 show water being raised by a bucket at- 

 tached to one end of a long pole, turning 

 on an axis with a heavy counterpoise at 

 the other end. In Egypt this is termed a 

 shadoof, and to this day, all along the Nile 

 banks, from morning to night, brown- 

 skinned peasants may be seen watering 

 their fields in precisely this way. Tier 

 above tier they ply their work so as to 

 raise water fifteen or sixteen feet on to 

 their land. By this simple contrivance it 



