(_c_) The average losses with canal water were ·0315 feet per hour, or 8·75 c. feet per second per million sq. feet.[52] With well water the figures were ·1096 and 30·5. The conclusion is that the silt in canal water reduces the losses by more than two-thirds. [52] This loss of 8·75 c. ft. per second was in water only about a foot deep. This confirms the conclusion arrived at in Chapter I, Art. 4, that the depth of water is not a factor of much importance. (_d_) With canal water the average loss decreased by 40 per cent. (from ·0491 to ·0293) in about four years. This was no doubt due to the effect of the silt. With well water the loss at the end of four years (·2293) was nearly four times as great as at first (·0591). This may have been due to removal of the finer particles of soil by the water, but the experiments were made at only one place, and were not conclusive. II. LINED TRENCHES. (_e_) With trenches lined with crude oil ¹⁄₁₆ inch thick, or with Portland cement ¹⁄₁₆ inch thick, or with clay puddle 6 inches thick, the “efficiency ratios,” as compared with unlined trenches, are respectively about 4·0, 5·7 and 5·7, the age of the lining being four years. The efficiency ratio is the inverse of the loss. Thus with an efficiency ratio of 3 the loss in the lined trench is 33 per cent. of that in the unlined trench. (_f_) The efficiency ratio in the case of oil may diminish at the rate of 10 per cent. per annum, but in the case of cement and clay puddle it tends to increase rather than to decrease. Assuming that the efficiency ratios are only 3·0, 4·5 and 4·5, and that the loss in an unlined channel is 8 c. feet per second per million sq. feet, the saving in water by using channels lined with oil, cement and puddle respectively would be 5·33, 6·25 and 6·25 c. feet per second. The average duty of the water at the canal head is about 242 acres, and the average revenue per acre is Rs 3·93. The revenue from 1 c. ft. of water at the canal head is thus Rs 950. Only about half the water reaches the fields (Chapter I., Art. 4), and the revenue from 1 c. ft. of water which reaches the fields is about Rs 1900. The mean of the above two sums is Rs 1425. If 6 c. ft. of water per second could be saved the revenue would be increased by Rs 8,550 per annum.