4 ELECTRICITY IN AGRILULTURE 
(4) In studying and observing sections of fir trees from 
different latitudes (60 deg. to 67 deg.) we have found a pecu- 
liarity in their yearly growth in thickness or year rings. 
They show in general a great difference in growth during 
different ages, but when due regard is paid to this fact, so 
that these differences may be eliminated, there remains 
another difference, which clearly must depend on the more 
or less advantageous nature of the atmospheric conditions 
of the year. 
These latter variations, taking into account principally the 
thickness of the year rings, show a periodicity in full agree- 
ment with the periods of the sun spots and the auroras— 
namely, a period of from Io to II years. By a comparison 
between sections of large pine trees from the Polar regions of 
lat. 67 deg. and from more southern latitudes (about 60 deg.), 
it will be seen that this periodic variation is much more 
pronounced the more nearly we approach the Polar regions. 
The circumstance that this periodicity agrees with that 
of the auroras will conduce to an investigation of a pos- 
sible connection betweeen the electrical current producing 
auroras and the year rings of these trees. As this peculiarity 
is more strongly developed in those regions of the earth 
where the electrical currents in question are of greater 
frequency and higher intensity, it indicates a connection 
between cause and effect which demands an investigation.* 
(¢) Inashort Paper entitled, “On the Periodic Variations 
in some Meteorological Phenomena, their Connection with 
the Changes of the Solar Surface and their Probable 
Influence on the Vegetation,”+ I have suggested, with a high 
degree of probability, that the harvest results in Finland 
show a periodicity which agrees with periodical variations 
in the sun spots and in the number of Polar lights. The 
greater the yearly number of sun spots and auroras, the 
more abundant is the harvest of seeds, roots, and grass.+ 
* This investigation is not yet published, 
+ Finsk tidfkrift, 1878, in Swedish. 
{ These harvest results also give evidence of the longer cycle period of 
about 58 years. 
