From AMS Glossary
An alternation of relatively cool-damp and warm-dry periods, forming an apparent cycle of about 35 years.
A belief in such a cycle of 35–40 years in Holland was known to Sir Francis Bacon in 1625, but it was rediscovered in 1890 by E. Brückner who regarded it as worldwide and attached great economic importance to it. Some studies have found quasiperiodic behavior on multidecadal timescales in a number of meteorological and related phenomena, but the existence of a cycle with this specific frequency remains controversial.
Brückner, E. 1890. Klimaschwankungen seit 1700. Nebst bemerkungen über die Klimaschwankugen der Siluvialzeit. Wien and Olmütz: Hölzel.