1868.] ( 479 ) 
IV. ARTIFICIAL IRRIGATION. 
Ir is undoubtedly one of the most important duties entrusted to 
man that he should learn to control the elements, and by bringing 
science and art to bear upon the works of Nature, to render them 
subservient to his will in promoting the general welfare of the human 
race, and in contributing to its every-day requirements. ‘Thus we 
see that destructive element, Fire, fairly brought into subjection, 
and forced to contribute to our wants in a thousand different ways. 
The Earth yields its hidden treasures for a similar purpose, and 
every description of soil which covers its surface has its allotted 
task to perform; whilst Air and Water, in addition to being abso- 
lute necessities of existence, have yielded the force and power with 
which they are invested to be applied in an infinite variety of ways 
to the wants of mankind. 
In many parts of the world where rain is uncertain, or only 
occurs at stated periods of the year, it would be impossible to carry 
on cultivation to an extent sufficient to produce food for the imha- 
bitants, without the aid of some artificial means by which water 
could be applied to the land, when most required by the growing 
crops. This fact seems to have been recognized many centuries ago 
in France, Peru, China, Spain, Italy, and in the East Indies, and 
at a still earlier date in Africa, systems of irrigation being clearly 
traced as having existed in the ages of the early histories of those 
countries. Few are perhaps aware of the extraordinary fertilizing 
powers of water even upon a barren sandy desert; but it has been 
proved by actual demonstration that the whole of Sindh, the greater 
part of which is marked on some of our maps of India as the 
“Great Desert,” might be turned into a perfect garden merely by 
diverting some of the waters of the Indus, which now run away 
into the sea, and applying them to the parched-up land. Agam, 
along the banks of the Suez Canal fertility has in many places suc- 
ceeded to a sterility of probably some thousands of years’ existence, 
and there is no practical reason why the entire desert, now for the 
first time cultivated only in parts, should not in course of years 
again fulfil the Divine mandate and “bring forth herbs, and fruit 
for the use of man.” 
Artificial irrigation consists in conducting water from some 
natural source of supply, such as rivers, springs, or lakes, by means 
of channels, or ducts, to the cultivated land which it is desired to 
irrigate. In some places this is done by throwing dams across 
rivers so as to raise their levels, and by forcing the water into a 
canal cut from the river at some point above the dam; the canal is 
then carried along the highest ground consistent with giving a 
sufficient slope to its bed to ensure a regular flow of water, from 
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