"On the Age of the Sun's Heat”

In March 1862, William Thomson publishes his essay, “On the Age of the Sun’s Heat,” followed on April 28 by his paper, “On the Secular Cooling of the Earth.” These constitute a two-pronged attack on the temporal assumptions undergirding The Origin of Species. Image: Photograph of William Thomson, Lord Kelvin. This image is in the public domain in the United States because its copyright has expired.