22 



METEOROLOGICAL OBSERVATIONS 



at Rothamsted contributes to the soil enough chlorine and 

 sulphuric acid to meet the requirements of most crops. 



Proportion of Rainfall percolating through Bare Soil. 



Alongside the large rain gauge, three percolation or drain 

 gauges were constructed in 1870. Portions of the undisturbed 

 soil, each one-thousandth of an acre in area, were isolated 

 from the surrounding soil by digging trenches and- building 

 brick and cement walls round the blocks of soil thus exposed. 

 The blocks were then undermined, and eventually carried 

 upon bars and plates of iron perforated to enable the percolat- 

 ing water to find its way into the collecting funnel beneath. 

 Thus in the end three blocks of undisturbed soil were 

 obtained, each one-thousandth acre in area, 20, 40, and 60 

 inches in thickness respectively, entirely isolated from the 

 surrounding soil, and the rain-water percolating through each 

 block is collected separately and measured like the rainfall. 



Table X. shows the average results obtained during the 

 forty-two years 1871-1912. 



TABLE X. Rainfall and Drainage at Hothamsted. 



