18 
THE SECRET OF THE BIG TREES. 
abdomens, giving them a moldy look. They seemed nearly as large 
as mice, and their speed of movement was positively alarming. With 
open nippers they rushed at our rulers and knives and tried them to 
see if they were edible. Sometimes they even nippd our hands, and 
more than once one of us uttered a sharp exclamation and jumped so 
as to throw knife and ruler to the winds and cause the waste of 10 
or 15 minutes in finding the place again. When we brushed the crea¬ 
tures away and looked at them from the normal distance they proved 
to be nothing but large black ants, about half an inch long. More 
pertinacious insects I never saw. Again and again I brushed an ant 
away to a distance of 6 or 8 feet, and watched that same ant turn the 
moment it alighted and rush back to the attack, and it did this not 
once but five or six times. 
During the 12 weeks that we were in the mountains in the two 
seasons of 1911 and 1912 we succeeded in measuring over 450 trees* 
79 of which were 2,000 or more years of age. The others were of 
various ages down to 250 years, for we measured a considerable num¬ 
ber of relatively young trees for purposes of comparison. The proc¬ 
ess of constructing the climatic curve from the data thus obtained is 
less simple than might at first appear. The obvious method is to 
ascertain the average growth of all the trees for each decade, from 
the earliest times to the present, and then to draw a curve showing 
how the rate has varied. The high places on such a curve will indi¬ 
cate times of comparative moisture, while the low places will indicate 
aridity. This method is too simple, however, for it takes no account 
of the fact that all trees grow faster in youth than in old age. Each 
species has its own characteristic curve of growth, as it is called. 
For example, during the first 10 years of its life the average Sequoia, 
washingtoniana grows about an inch in radius, that is, it reaches a 
diameter of 2 inches; at the age of 200 years the average tree adds 
about nine-tenths of an inch to its radius each decade; at the age of 
500 years about six-tenths of an inch; and at the age of 1,700 only 
three-tenths. These figures have nothing to clo with the rainfall, but 
indicate how fast the tree might be expected to grow if they were 
subject at all times to the average climatic conditions, without any 
variations from year to year. 
Evidently, if we desire to institute a fair comparison between the 
growth of a tree 200 years old and of one 1,700 years old, we must 
either multiply or divide by 3. By applying such corrections to 
each measurement among the 105,000 which made up the work of our 
two summers, we are able to eliminate the effect of differences in the 
ages of the trees. The process is purely mathematical and depends in 
no respect upon the individual ideas of the computer. In addition to 
the correction for age, there is another, which I have called the cor¬ 
rection for longevity. What sort of tree is likely to have a long life* 
