1100 1000 900 800 700 GOO 500 400 300 200 100 BC AD 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 
20 
THE SECRET OF THE BIG TREES. 
or 1,000 years. Hence, in order to 
institute a fair comparison between 
the rate of growth in the days of 
Darius and now it is necessary to 
make still further corrections. This 
process, like the other, is purely 
mathematical. The only difficulty is 
that in order to secure high accuracy 
a large number of trees of all ages 
is necessary. It is easy to obtain 
plenty of young trees under 2,000 
years of age, but older ones are so 
scarce that we have not obtained 
enough to render the corrections 
fully exact. Hence in the earlier 
parts of the curve, the details are 
less exact than could be desired, and 
the fluctuations are relatively too 
great, since they are not smoothed 
out by the use of a large number of 
trees. In the portion of the curve 
since about 100 B. C., however, the 
fluctuations for minor periods and 
also for centuries show no appre¬ 
ciable errors except such as are due 
to special accidents. Nevertheless 
there is some doubt as to whether 
the curve as a whole in its descent 
from early times down to the pres¬ 
ent should slope more or less than is 
here shown. 
The accompanying diagram sums 
up the results of our work on the 
big trees as compared with the re¬ 
sults of work of an entirely differ¬ 
ent kind upon the climatic fluctua¬ 
tions of Asia. Horizontal distance 
indicates time; the diagram begins 
at the left-hand end with 1300 B. C., 
and ends on the right with 1900 
A. D. Vertical distance indicates a 
greater or less amount of rainfall 
or more or less favorable condi¬ 
tions of plant growth. The solid 
line is the curve of the sequoias. 
During the periods where it is high, 
