The astronomer A.E. Douglass is generally recognized as the founding father of dendrochronology. He studied
tree rings in the search for evidence that solar variation (as seen in sunspots) is reflected in climate variation. He was
convinced that his quest was successful. Analysis of some of his early data using Fourier decomposition and comparison
of tree-ring periodograms with those based on known solar cycles suggests that the cycles he found may not exist or may
not be of pure solar origin. The findings here reported suggest a much stronger influence of tides on the tree-ring records
than commonly considered. Douglass’s great merit as the pioneer of tree-ring dating in archeology and tree-ring-based
climatology remains unaffected by the findings here presented.