FORESTS AND RAINFALL. 1g! 
water, and therefore that may be eliminated for our present 
purpose. The fraction imbibed by the surface of the soil is 
the same in forests as in agricultural land; the fraction 
evaporated on or in the soil is less in forests; the fractions 
retained and evaporated by vegetation, and absorbed for its 
growth and transpiration, must consequently be greater. ‘This 
is known to be the fact, and the difference between the amount 
of evaporation from crops and that from forest can even be 
measured. 
There must, therefore, be zz the air over forests a much larger 
amount of watery vapour than over any other cultivated ground, 
and this has been demonstrated to be actually the case, notably 
by the meteorologist Fautrat, who states, further, that this 
moisture is more pronounced over evergreen than over deciduous 
woods. It is very difficult to measure the transpiration from 
wooded areas. The only results that can be quoted are those 
of the Austrian, Dr Franz R. von Hdéhnel, who, in the course of 
observations continued from 1878 to 1880, ascertained that a 
hectare of beech forest, 115 years old, absorbed daily from 25,000 
to 30,000 litres of water. 
The theory of the dampness of the air over forests is further 
borne out by aerial meteorologists, amongst others by Renard, 
who asserts that when aeronauts pass over wooded land there is 
always a well-marked fall of the balloon. This fact has also 
been observed above the forest of Orleans by many military 
aeronauts. 
3. FOREST INCREASES RAINFALL. 
When a mass of damp, hot air strikes against this column of 
damp, cold air rising from woods, at least a part of its watery 
vapour is likely to condense into the form of mist or small rain, 
thus causing more rainfall over wooded areas than over bare or 
cultivated plains. This has been proved by experiments at 
Nancy and other parts of France, Germany, Russia, and even 
India. But the extent of the influence of the forest on the 
rainfall is, of course, difficult to measure. From what has been 
shown, it is obvious that forest, when it has sufficient masses of 
water at its disposal, works like an extremely powerful pump, 
bringing the water up from a depth where it had become useless 
to vegetation, and sending it back into the current of atmospheric 
circulation. 
