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A scientist described in the September 1946 issue of True: The Men's Magazine kept a chart on his lab wall that looked like a stock graph. The peaks and valleys represented his mood cycle. High weeks, he'd "feel equal to tackling tigers with his bare hands." Low weeks, he'd "sell out for a nickel." "Don't start an argument with me today!" he told writer Donald G. Cooley. "I'm scraping bottom of my mood cycle."

The method: draw a scale from elation to depression, one column per day, and plot a dot each evening for your emotional tone. Connect the dots after a few weeks, and look for a wave. According to the article, the average cycle runs five or six weeks; once two or three full loops confirm your rhythm, you can transfer it to a calendar and read off your mood a month or two ahead.

The underlying research was conducted by Professor Rex G. Hersey at the University of Pennsylvania, who spent a year tracking the emotional fluctuations of public utility workers.…