5.1 Tree Rings and Mathematical Series
67
more extended version of the newspaper article appeared in the Netherlands in
the form of a separate publication. He had succeeded in collecting an almost
continuous series of measurements of the thickness of annual rings between
1770 and 1880 for the trees in the Trier area. Those thicknesses correlated very
well with meteorological data as far as available, such as the number of days of
rain in each year or the total amount of precipitation. He also found a clear
periodicity of 12.4 years and noted that this was significantly different from
the solar cycle of about 11 years which is related to the number of sunspots.
He gave his lecture in California because he wanted to point out that with the
use of sequoia trees one could collect this kind of data over a thousand or more
years. Incidentally, the period of 12.4 years has never been confirmed, as far as
I am aware.
Kapteyn also worked with his brother Willem (Figs. 5.1) in Utrecht on a
mathematical problem. This concerned the properties of certain mathematical
Fig. 5.1 Willem Kapteyn, brother of Jacobus Kapteyn, was a professor of mathematics
at Utrecht University. This picture comes from the Album Amicorum, presented to H.G.
van de Sande Bakhuyzen on the occasion of his retirement as professor of astronomy
and director of the Sterrewacht Leiden in 1908 [47]
67
more extended version of the newspaper article appeared in the Netherlands in
the form of a separate publication. He had succeeded in collecting an almost
continuous series of measurements of the thickness of annual rings between
1770 and 1880 for the trees in the Trier area. Those thicknesses correlated very
well with meteorological data as far as available, such as the number of days of
rain in each year or the total amount of precipitation. He also found a clear
periodicity of 12.4 years and noted that this was significantly different from
the solar cycle of about 11 years which is related to the number of sunspots.
He gave his lecture in California because he wanted to point out that with the
use of sequoia trees one could collect this kind of data over a thousand or more
years. Incidentally, the period of 12.4 years has never been confirmed, as far as
I am aware.
Kapteyn also worked with his brother Willem (Figs. 5.1) in Utrecht on a
mathematical problem. This concerned the properties of certain mathematical
Fig. 5.1 Willem Kapteyn, brother of Jacobus Kapteyn, was a professor of mathematics
at Utrecht University. This picture comes from the Album Amicorum, presented to H.G.
van de Sande Bakhuyzen on the occasion of his retirement as professor of astronomy
and director of the Sterrewacht Leiden in 1908 [47]