more effectively than the conductivity which Kelvin assumed, and he stated that "much internal fluidity would practically mean infinite conductivity for our purpose." Kelvin rejected this idea as there was no evidence of tidal deformation of the Earth's crust, and in response Perry made a reference to Kelvin's favourite demonstration of the slow deformation of shoemaker's wax to illustrate the supposed qualities of the presumed luminiferous aether thought then to be necessary to transmit light through space. Perry wrote that "the real basis of your calculation is your assumption that the solid earth cannot alter its shape ... even in 1000 million years, under the action of forces constantly tending to alter its shape, and yet we see the gradual closing up of passages in a mine, and we know that wrinkling and faults and other changes of shape are always going on in the earth under the action of long-continued forces. I know that solid rock is not like cobbler's wax, but 109 years is a long time, and the forces are great." The failure of the scientific community to accept a fluid interior to the Earth held back ideas in geology until the concept was revived by proponents of continental drift, and even in the 1960s geophysical models were still being constructed on the basis that the Earth was solid. References External links Irish engineers Irish mathematicians Foreign advisors to the government in Meiji-period Japan Foreign educators in Japan British expatriates in Japan 1850 births 1920 deaths People from County Londonderry Fellows of the Royal Society Presidents of the Physical Society