38 Quantity of Water Consumed in Irrigation. 



slight excavation, might at first sight be taken as opposed 

 to the foregoing deductions regarding the extent of percola- 

 tion ; but the conditions under which tanks can be suc- 

 cessfully formed are essentially different from those pertain- 

 ing to an ordinary canal. It will suffice here to remark 

 that generally those conditions which are favourable to the 

 construction of a tank restrict the escape of subsoil water, 

 while those favourable to a canal facilitate its escape ; and 

 on the free escape or otherwise of the subsoil water, it 

 depends whether percolation is much or little. 



Y. — Application of Results to other Countries than 



India. 



25. Before showing how to apply the foregoing deduc- 

 tions to canals in other countries than India, it will be 

 well to examine the two cases briefly noticed above (see 

 par. 10) and their bearing on the conclusions drawn by the 

 author. In the first instance, with a larger supply in the 

 Ganges canal in the cold season of 1868-69 by 5 per cent, 

 than that in the cold season of 1875-76, the area irrigated 

 was 39 per cent, larger. It is clear that either there was 

 less waste or the crops received less water in 1868-69 — pro- 

 bably both. That the crops received less than the usual 

 quantity of water in 1868-69 is evident from the remark by 

 the Superintending Engineer (Colonel Brownlow, RE.) — 

 " I have no hesitation in saying that, but for the timely and 

 providential fall of rain in the end of January, there would 

 have been failure of crops, and consequent bitter distress 

 over considerable areas."* There was an unusually large 

 supply of water (6000 cubic feet per second in October, 

 1 868) at the commencement of the season, allowing a larger 

 area than in any previous year being watered ; but when, 

 in January, 1870, the supply fell to 4200 cubic feet per 

 second, the canal could not have supplied the wants of the 

 irrigators had not rain fallen. It is thus clear that the 

 crops received less than their normal supply of water — 

 probably an average of three waterings was given instead 

 of four, the usual number. 



26. Taking the number of days in the season for con- 

 venience of comparison, the same as in 1875-76 (there may 



* Professional Papers on Indian Engineering, Vol. VII. (Roorkee, 1870), 

 page 303. 



