41 3 REPORT OF THE COMMISSIONERS OF 



" The method which I have employed for solving the problem, differs completely 

 from those used by other experiments. Thus, my method consists in gaging the 

 amount of water issuing from under-drains, draining a certain known area, and in 

 comparing the amount of drainage water with the amount of rainfall on the same 

 surface, the difference between the two giving the quantity of water evaporated. 



" In order to successfully apply this method, two principal conditions must 

 be observed: 



"(i) No other water should be allowed to come in contact with the earth except 

 the rainfall directly upon the surface. For my experiments, a piece of land 12,300 

 square meters, situated upon the highest part of a clay plateau, was selected. No 

 water could reach this area from the neighboring soil. 



"(2) It is necessary that all the water which is not evaporated be received by the 

 drains, this second condition being equally important with the first. In the area 

 experimented upon, the sub-soil is so compact that the drains, which are laid at a 

 depth of forty-seven inches and thirty-three feet apart, must necessarily receive all 

 the water which penetrates beneath the surface, and which is not evaporated. 



■"The experimental field fulfills all the necessary conditions. It has no trees. In 

 1867 two-fifths of the area was planted to potatoes, two-fifths to wheat, three- 

 twentieths to Lucerne-grass, and one-twentieth in ditches carrying the drainage water. 

 In 1868, two-fifths were in wheat, two-fifths in clover, three-twentieths in Lucerne- 

 grass and one-twentieth in ditches. Gagings of the drainage water were made at 

 noon each day at a point below where all the drains come together. 



"The following table gives the quantity of rainfall for each month of the years 

 1867, 1868, the run-off of the drains and the quantity of water evaporated. These 

 figures show that in 1867 the evaporation was 68.75 P er cent., and in 1868 73.17 per 

 cent, of the rainfall, or making certain corrections because of the water in the soil, we 

 have the final figures for 1867, 70.75 per cent, and for 1868, 70.17 per cent." 



