14 
been inserted in our figures alongside of the curves. So 
for instance for the Main-wood (fig. II) for the years 
1879 and 1878, 7 trees have contributed; from 1877— 
1875, 11 trees; from 1874—1870, 15; from 1869 to 1841, 
16 etc, 
5th. Some measurements have been made on the trans- 
verse section of the trees, while lying in the wood or 
elsewhere. Mostly however discs from 3—7 centimetres 
thick were obtained. These were then measured at leisure 
at home. In the beginning each disc was measured along 
6 radii; afterwards this number was lowered to 3, in 
many cases to 2. À few of the trees have been only 
measured once. The measures were made with a milli- 
meter scale. À magnifier was used in reading this scale 
to the nearest tenth of a millimeter. 
6th. Parallelism of wood-growth with sun-spots, might 
readily be supposed to exist if we compare for instance 
the wood-growth of the trees represented in fig. VII with 
Wolf's relative numbers. As however according to the 
Main- and Moselle-trees such parallelism does not show 
in the same manner in the 18th century, I think the 
probability of a real connection very slender. 
7th. The inspection of even a moderate number of 
wood sections shows that there are influences which, for 
longer periods, cause a gradual change in the wood- 
growth as measured by the breadth of the ring, changes 
which in many cases are different for different trees. Such 
must be the influence of age. Such an effect will also 
be introduced if a tree gets more and more hindered by 
surrounding trees etc. These slow changes are very apt 
to vitiate to some extent, our conclusions about the 
changes of shorter period, especially where we combine 
several trees into a normal. Ît is in order to get rid 
of these gradual changes that I adopted the method of 
expressing the growth in percents over and below the 
