COLLECTION OF SECTIONS. 37 
used. No. S17, Picea excelsa, marked “4105-5,” was cut in May 
1909, in the same locality as S 14 and shows a similar rhythm. Its 
center was in 1777. No. S 18 was a small section marked “4131-a-12.” 
It was cut in October 1910, in latitude 58°, well to the west of the 
others. Its radius measured only 2 inches. The average diameter of 
the other sections was about 12 inches. 
On page 115 will be found the means of these sections, with two 
extrapolations, one from 1820 to 1848 and the other from 1820 to 1878. 
This curve will be found plotted in figure 8. It has been corrected for 
age and reduced to percentages by dividing by the readings of a 
straight line extending from 1.90 mm. in 1820 to 0.70 mm. in 1910. 
This corrected set has been smoothed by Hann’s formula and will be 
found plotted in figure 23. 
EBERSWALDE (PRUSSIA) GROUP. 
These 13 trees were cut and sections prepared for me by the kindness 
of Professor A. Schwappach of Eberswalde. They were all Pinus sil- 
vestris planted about 1820 to 1830, exactly alike in height and size, 
with tall, straight, clear trunks about 10 inches in diameter and bushy 
tops. The land is a gently rolling country with a slight northerly slope, 
leaf-covered ground, a sandy soil with loam on top, and an elevation 
above the sea of 200 to 300 meters. The height above the city level 
was 200 feet or so; the locality was south and west of Eberswalde 
station. The trees cut were scattered along a quarter of a mile and so 
did not represent any close grouping. Their rings show almost identical 
records; 2 to 10 in every decade have enough individuality to make 
them recognizable in every tree. 
_ On the first examination of these sections in November 1912, it was 
evident that their growth follows with fidelity the sunspot curve since 
1830. This may be traced in the curves below and in the accompanying 
photographs of two of the sections in plate 8. It will be seen at once 
that there is a rhythmic sway in the growth, groups of large rings 
alternating with small ones. The arrows placed in the photographs 
mark the years of maximum sunspots. Taking the group as a whole, 
the maximum growth comes within 0.6 year of the sunspot maximum. 
To one maximum alone they fail to respond, namely, 1894; instead of 
rising, the curve drops in 1892, 1893, and 1894. I have tried to find 
cause for this, but wasinformed by Professor Schwappach that therewere 
no fires, pests, or other known causes for it except climatic conditions.! 
1Schwappach. Zeitschrift Forst- und Jagdwesen, September, 1904. A recent bulletin of 
the Mellon Institute, by J. F. Clavenger, entitled, ‘Effect of the soot in smoke on vegetation,” 
suggests at least a possibility. Clavenger shows photographs of tree sections in the neighborhood 
of iron mills, in which the growth is normal until the smoke from the mills pours over the forest, 
and then the rings rapidly decrease in size, It would solve the puzzle if it could be shown that 
smoke from the iron and brass works in the neighboring city came over the forest of Eberswalde 
more abundantly at about this time. Dr. Schwappach writes that the manufactories and repair 
shops are 3 km. distant and in his opinion the decrease in growth can not be due to smoke from them. 
