I sat beside him [Kelvin] last night at Trinity and he had to listen. I knew beforehand that he would not read my documents and he hadn’t but I gave him a lot to think of and his pitying smile at my ignorance died away in about 15 minutes. I think he will now really begin to consider the matter. Geikie [the geologist Archibald Geikie] was opposite, his eyes gleaming with delight.

The scientific journal Nature eventually published Perry’s article on January 3, 1895. The report started in an apologetic tone: “I have sometimes been asked by friends interested in geology to criticize Lord Kelvin’s calculation of the probable age of the earth. I have usually said that it is hopeless to expect that Lord Kelvin should have made an error in the calculation.” Perry then went on to express his personal reservations about the methodology used in geology at the time: “I dislike very much to consider any quantitative problem set by a geologist. In nearly every case the conditions given are much too vague for the matter to be in any sense satisfactory, and a geologist does not seem to mind a few millions of years in matters relating to time.” Finally, Perry explained what had nevertheless convinced him to take on the daunting task of challenging Kelvin: “His [Kelvin’s] calculation is just now being used to discredit the direct evidence of geologists and biologists, and it is on this account that I have considered it my duty to question Lord Kelvin’s conditions.”

Perry focused most of his attention on one of Kelvin’s basic assumptions: that the Earth’s conductivity was the same at all depths. In other words, Kelvin assumed that heat was transported with uniform efficiency, be it at a depth of one mile or a thousand miles. This hypothesis was crucial. Just as a forensic investigator can determine the time of death by measuring the temperature of the corpse, Kelvin used this assumption to determine the cooling age of the Earth, by measuring by how much the temperature within the Earth increased with each foot of depth. Kelvin’s calculation showed that if the Earth were older than about one hundred million years, then the temperature would rise with depth more slowly than was actually observed, since the cooled skin would be thicker.

Perry wondered, what if instead of being the same everywhere, heat transport in the deep interior were more effective than near the surface? Clearly, in that case, the bottom of the Earth’s outer skin could be kept warmer for much longer. In particular, Perry showed that if the Earth’s interior happened to be partly fluid, then, just as with water heated in a deep pot, heat could be convected to the surface crust so efficiently (by the fluid itself) that the age estimate could be extended even to three billion years. He then concluded his article by addressing the arguments based on the age of the Sun and on the Earth’s spin, but there was nothing really new in his discussion of these topics. Regarding the question of the tidal retardation of the Earth’s rotation rate, Perry called attention primarily to George Darwin’s demonstration that even a solid Earth could still alter its shape.

At first, Perry’s article (in its prepublication circulated form) drew a response not from Kelvin himself but from his self-appointed “bulldog”: Peter Guthrie Tait. In an offensively dismissive letter, Tait wrote to Perry on November 22, 1894: