In 1875 and 1878, Jevons read two papers before the British Association which expounded his famous "sunspot theory" of the business cycle. Digging through mountains of statistics of economic and meteorological data, [u]Jevons argued that there was a connection between the timing of commercial crises and the solar cycle.[/u] The basic chain of events was that variations in sunspots affect the power of the sun's rays, influencing the bountifulness of harvests and thus the price of corn which, in turn, affected business confidence and gave rise to commercial crises. Jevons changed his story several times (e.g. he replaced his European harvest-price-crisis logic with an Indian harvest-imports-crisis channel). However flimsy his explanations, Jevons believed that the periodicity of the solar cycle and commercial crises -- approximately 10.5 years, by his calculations -- was too coincidental to be dismissed. Needless to say, all this was a bit on the cranky end and, ultimately, the statistics did not bear him out. Nonetheless, it remains a significant piece of work as this was perhaps the first time that the phenomenon of the business cycle was identified. Economists had long been aware that business activity had its ups and downs, but not that they necessarily followed any regular pattern. They generally believed that "crises" arrived haphazardly, punctuating the smooth advance of the economy at irregular intervals. Jevons was perhaps the first economist to argue that the phases of business activity had a regular, measurable and predictable periodicity.
http://cepa.newschool.edu/het/profiles/jevons.htm
