10 
know that the rainfall, in the case of a mountain, increases up 
to the altitude of 1000m. and then decreases above that line. 
We can approximately calculate the rainfall of a flank of a 
mountain at any altitude, if we but know the rate of in- 
crease of rainfall for each 100m. The stations at Shiraito and 
Omiya are almost in a line from the top of the mountain. And 
therefore the difference of rainfall observed at these two stations 
will tell us the rate of increase of rainfall due to the altitude. 
The rate of increase in every 100m. thus calculated is 72mm. 
in annual mean of rainfall. Applying this rate to each station, 
we calculate the annual mean rainfall of the five directions at 
an altitude of 1000m., which amounts are shown in the follow- 
ing table. 
Tab. II. 
Annual mean 
of 1000m. 
rainfall at the altitude 
on the Shiraito side. 
2936 
mm. 
?? 
V 
Omiya side. 
2889 
V 
V 
Goten side. 
2596 
V 
Nakano side. 
2942 
Shoji side. 
2534 
In tins table we see the Nakano side leads in the amount 
of rainfall, next come the Shiraito and Omiya sides, while the 
Goten and Shoji sides have the least. This climatic character, 
however, seems to have but slight significance in explaining the 
present vegetation ; for vegetation does not depend so much upon 
rainfall, as it does upon the soil, ground water, and humidity, 
which will be considered later. 
However great the rainfall, if it comes all at once and 
runs away very rapidly, it will favour growth far less than 
frequent light rains. So the frequency of the rains should be 
taken into consideration. 
