12G Composition of Waters of Land- Drainage and of Rain. 



which was adopted by Mr. Parkes,* founded on the observations 

 of Mr. Dickinson, the eminent paper-maker. That gentleman 

 had for many years kept registers of the ordinary and Dalton 

 rain-gauge. The object of the last named instiument is to ascer- 

 tain the quantity of rain which peneti'ates the soil to a given 

 depth. Now it must be remembered that although all the rain 

 that falls must necessarily be disposed of somewhere, there is 

 another influence besides filtration at work, and that is evapora- 

 tion. In the hot seasons of the year a great deal of water is thus 

 thrown back into the air, and this is especially the case where, 

 as in ordinary agriculture, the land is covered with plants, which 

 taking up the moisture of the soil by their roots, exhale it by 

 their leaves, and thus most materially increase the ordinary 

 evaporation from the soil.f 



The Dalton rain-gauge consists of a metallic vessel of about 3 

 feet deep, sunk into the ground, level with the surrounding earth, 

 but furnished with a rim to prevent the passage into it of any 

 water except that which absolutely falls upon its surface. It is 

 made — like other rain-gauges — of a givea superficial area, but 

 the chief peculiarity in it is, that it is filled with earth, so as to 

 represent the soil with which it is desired to compare the results. 

 In the case liow alluded to, the soil in the gauge was covered 

 during the whole period with grass. 



An arrangement is made by which the water which penetrates 

 to the l)ottom of the earth — a distance of 3 feet — is measured at 

 stated periods, as in the ordinary gauge. Now as evaporation 

 from the surface will dispose of some portion of the water which 

 falls in rain, it is obvious that the quantity which penetrates to 

 the bottom of the Dalton gauge would be less than that collected 

 in an ordinary gauge. In fact the results of this gauge are the 

 measure of the quantity which, in a similar soil drained to the 

 same depth, would be disposed of by the drains. We have but 

 to compare the indications of the two gauges for any given period, 

 to know at once how much of the rain-fall is thrown into the 

 air by evaporation, and how much runs off by the drains. The 

 use made by Mr. Dickinson of this register was in no way con- 

 nected with agriculture, but the results are precisely such as we 

 should desire to possess in dealing with the question in hand. 



In a Table, which I here take the liberty to reprint, Mr. Parkes 

 gives the quantity of rain and percolation in each year of a series 

 of 8 years, as ascertained in Mr. Dickinson's gauges. In the 

 5th column the quantities are given in tons per acre : — 



* See his ' Essays on the Philosophy and Art of Land Drainage ;' Journal of 

 the Royal Agricultural Society of England, Vol. V., Part I. 



t Messrs. Lawes and Gilbert, who have made some experiments on this subject, 

 found that the quantity of water thus exhaled from a given space of ground is 

 very large indeed, amounting to more than 100 times the weight of the crop at the 

 time of maturity. 



