66 H. DEANE. 



The upper line on each diagram represents saturation. Vertical 

 measurements are in inches and tenths of inches, and the distance 

 of any point on the " drought line," as it is convenient to call it, 

 from the line of saturation, is intended to represent the number 

 of inches or tenths of inches of rainfall required to restore the 

 saturated condition on that particular day. The rises represent 

 rainfalls. The drought line cannot of course rise above the line 

 of saturation. If at any time when rain begins, it only requires 

 a certain quantity to complete saturation, any balance of a rain- 

 fall larger than this quantity must be treated as surplus and not 

 recorded in the diagram. It may however, be entered in figures 

 below. This quantity as a rule, flows off or drains away through 

 the soil, and is useless as regards the particular area on which it 

 has fallen, though it may be collected and made available for 

 water supply, and it helps to keep up the flow of rivers and streams, 

 but that is a different question altogether. 



Starting now at a point where complete saturation has been 

 effected and rain has ceased to fall, the drying process is shown 

 by the descending line, the vertical descent for each day is the 

 amount of drying which has taken place. This is dependent on 

 the weather conditions, temperature, dryness of the air and the 

 existence or otherwise of wind. 



At starting, the amount for the first day must bear some definite 

 proportion to the evaporation from water under the particular 

 conditions. As stated already this evaporation must vary accord- 

 ing to the weather conditions. It is greatest in summer and when 

 the air is dry and wind is blowing, and least under the reverse 

 conditions. In making the diagrams however, I have found it 

 convenient to use the calculated averages for each month. This 

 is of course not quite correct, but the general results will not be 

 far wrong. 



As the ground dries, the rate of evaporation slackens because 

 the moisture has to be drawn up from increasing depths; the daily 

 drops of the drought line becomes less, and the effect is to produce 



