582 



SCIENCE. 



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



it not that the glaciers of the Alps are 

 melting then, and the great torrents of the 

 Dora Baltea and Sesia can be counted on 

 for a volume exceeding 6,000 cubic feet 

 per second. 



Lombardy is in no respect worse off than 

 Piedmont for the means of irrigation ; and 

 its canals have the advantage of being drawn 

 from the lakes Maggiore and Como, exer- 

 cising a moderating influence on the Ticino 

 and Adda Eivers, which is sadly^wanted 

 on the Dora Baltea. The Naviglio Grande 

 of Lombardy is drawn from the left bank 

 of the Ticino, and is used largely for navi- 

 gation, as well as irrigation. It discharges 

 between 3,000 and 4,000 cubic feet per 

 second, and nowhere is irrigation probably 

 carried on with less expense. From be- 

 tween Lake Maggiore and the head of the 

 Naviglio Grande a great new canal, the 

 Villoresi, has been constructed during the 

 last few years with head sluices capable 

 of admitting 6,700 cubic feet per second, 

 of which, however, 4,200 cubic feet have 

 to be passed on to the Naviglio Grande. 

 Like the Cavour Canal, the Villoresi crosses 

 all the drainage coming down from the 

 foothills to the north. This must have en- 

 tailed the construction of very costly works. 



IRRIGATION IN NORTHERN INDIA. 



It is in India that irrigation on the larg- 

 est scale is to be found. The great plains 

 of northern India are peculiarly well 

 adapted for irrigation, which is a matter 

 of life and death to a teeming population 

 all too well accustomed to a failure of the 

 rain supply. 



The Ganges, the Jumna and the great 

 rivers of the Punjab have all been largely 

 utilized for feeding irrigation canals. The 

 greatest of these, derived from the river 

 Chenab, and discharging from 10,500 to 

 3,000 cubic feet per second, was begun in 

 1889, with the view of carrying water into 

 a tract entirely desert and unpopulated. 



It was opened on a small scale in 1892, was 

 then enlarged, and ten years after it irri- 

 gated in one year 1,829,000 acres, support- 

 ing a population of 800,000 inhabitants, 

 colonists from more congested parts of 

 India. 



The Ganges Canal, opened in 1854, at a 

 time when there was not a mile of railway, 

 and hardly a steam engine within a thou- 

 sand miles, has a length of about 9,900 

 miles, including distributing channels. It 

 was supplemented in 1878 by a lower canal, 

 drawn from the same river 130 miles fur- 

 ther down, and these two canals now irri- 

 gate between them 1,700,000 acres an- 

 nually. On all these canals are engineer- 

 ing works of a very high class. The orig- 

 inal Ganges Canal, with- a width of bed of 

 200 feet, a d'^pth of ten feet, and a maxi- 

 mum discharge of 10,000 cubic feet per 

 second, had to cross four great torrents be- 

 fore it could attain to the watershed of the 

 country, after which it could begin to irri- 

 gate. Two of these torrents are passed 

 over the canal by broad super-passages. 

 Over one of them the canal is carried in a 

 majestic aqueduct of fifteen arches, each of 

 fifty feet span ; and the fourth torrent, the 

 most difficult of all to deal with, crosses 

 the canal at the same level, a row of forty- 

 seven floodgates, each ten feet wide, allow- 

 ing the torrent to pass through and out 

 of the canal. 



Elsewhere there are rivers in India, rising 

 in districts subject to certain heavy period- 

 ical rainfall, and carrying their waters on 

 to distant plains of \ery uncertain rainfall. 

 At a small expense channels can sometimes 

 be constructed drawing off from the flooded 

 river water sufficient thoroughly to saturate 

 the soil, and render it fit to be ploughed 

 up and sown with wheat or barley, which 

 do not require frequent watering. The 

 canal soon dries up, and the sown crop must 

 take its chance ; but a timely shower of rain 

 may come in to help it, or well irrigation 



