49 
Ï think we can by consulting the registers kept by 
nature herself in our trees. For there are plenty of trees 
all over the world and many of them attain to a con- 
siderable age. By them we may get data not only of 
prehistoric, but even of geological time. 
The idea of conceiving the trees as natural registers 
seems so natural that it must have occurred to several 
minds. 
Even the use of the growth-rings as a means of finding 
out a connection between the weather in past years and 
the tree-growth is certainly not new. — Meanwhile I 
was unable to find any regular investigation on the subject 
extending over a period of more than just a few years. — 
This gives me the courage to lay before you my very 
fragmentary study, which, however, was carried through 
with the definite aim of finding out some regularity. 
Ï have confined myself entirely to the investigation of 
oak-trees. Other kinds of trees may prove preferable 
for definite purposes. But as the limited time at my 
disposal made a choice necessary, I naturally chose the 
kind of wood which in our parts is easily obtainable from 
all sorts of localities and which usualiy is not cut down 
at so early an age as our other trees. 
Suppose such an oak-tree cut down at the present 
moment and suppose that we get a cross-section of that 
tree at some distance from any place where a root 
branches off. The section will then show a series of 
pretty regular concentric rings, which we call the 
growth-rings. The wood between the bark and the 
first ring will represent the growth during the year 
1908. The growth during the year 1907 will be 
represented by the wood between the 1st and 2nd ring 
counting from the outside towards the centre and so on. 
We thus have only to know the year in which the tree 
