KELATION OF EVAPORATION TO FORESTS. 



97 



tation by the woods. Fig. 50 exliibitts the distribution of the ev;ii">o- 

 ration for the year. The upper line represents the progress for the 

 water surface in the open air, the lower that for the same in the woods. 

 The shaded space indicates the saving, in inches, of a sheet of water 



Flu. 50. — Monthly cvapuratiou iu tliu liflds (upper curve) aud woods (lower curve). 



which is affected by tlie cover of the forest in lessening evaporation. 

 The evaporation and its saving by the woods are botli greatest in IMay 

 and June and they decrease symmetrically on each side of these months. 

 The amount in the winter months is very sm;ill, and it is, moreover, 

 somewhat uncertain, as it is difficult to make the observations at that 



P'lO. 51. — Percentage of evajjoratiou iu the woods as coiuparod with that iu open fields. 



season. The annual evai)oration in the A\oods is 44 per cent of that in 

 the fields. Fig. 5L represents the percentage for the different months 

 of the year. The upper straight line stands for 100 per cent, or the 

 evaporation in the fields during the year, and the curve below repre- 

 sents the percentage in the woods. The shaded space is the percentage 



100 



Fio. 52.— Ratio of evaporation from water surface in field (upper curve) and forest (lower curve) to 



precipitation (toj) line). 



of lield evaporation which is saved by the foics-t. This covers a full 

 half of the diagram, with some addition to this from May to November. 

 It is also interesting to compare the ev;ii)oratioii iVoiii a water surface 

 with tlie precii>itation from month to month. Tliis is done in Fig. 52. 

 12444— No, 7 7 



