Carlos Garcia-Mata & Felix Ira Shaffner (1934) - It is common knowledge that people from all walks of life and every station of society participated in what is now generally agreed was - considering the number of persons and transactions involved - the greatest speculative mania of modern times. The bursting of this speculative bubble at the end of 1929 affords an excellent opportunity for something analogous to an experiment on the correlation of turning points in solar and speculative activity. Stock prices had experienced an extraordinary rise from a level of around 100 in 1924 to approximately 320 in the first half of 1929.
[…] With this in mind, we compared monthly data of speculation in 1929 with variations in solar phenomena for the same year […] In the upper part of the chart the solar-radiation curve is plotted upside down to help visualize the inverse correlation. Another comparison between business and solar data was made employing an index computed since August, 1924, by the Mount Wilson Observatory. This is an index of a part of the solar spectrum, the ultraviolet rays, which, it will be remembered, vary within a much wider range than the total solar radiation curve. This index was reduced to a 12-month moving average to make it comparable with the rest of the chart. Although the period is so short that nothing statistical can be deduced, the existence of a direct correlation with the business curve is apparent […] For an index of American speculative sentiment, we chose Professor W.L. Crum's index of industrial stock prices, known as “Barron's Averages, because they are constructed to portray the speculative movement of stock prices rather than the trend of investment prices.”
[...] A glance at the chart will show a striking similarity in the date of the turning points. Furthermore, contrary to expectations, the behavior of the two curves during the whole year is similar. The lowest prices for common stocks in the New York and London Stock Exchanges were reached in the first half of July 1932 [...] The [third] chart shows the curious fact that the recession in the last quarter of 1932 is also visible in the solar curve. And it is interesting to note that the solar curve makes a second low in February, 1933, turning up again in the following months. Although this is a fact, too much should not be expected of comparisons for the year 1933 because, except for clear solar changes which are sudden and which can be associated with the turning points, it is too much to hope for an exact month-to-month correlation. In the years in which the speculative curves moved steadily up or down, such as in 1930-31 and previous to 1929, no clear moth-to-month relation has been found between solar and speculative short swings, except for the seasonal movements of the speculative curve in the down swing, which perhaps can be associated with the similar seasonal variations of the solar-terrestrial physical curves such as magnetic activity and aurora borealis.