Pronouncements later proven to be false

Like many scientists, he did make some mistakes in predicting the future of technology.

Circa 1896, Lord Kelvin was initially skeptical of X-rays, and regarded their announcement as a hoax.^[50] However, this was before he saw Röntgen's evidence, after which he accepted the idea, and even had his own hand X-rayed in May 1896.^[51]

His forecast for practical aviation was negative. In 1896 he refused an invitation to join the Aeronautical Society, writing that "I have not the smallest molecule of faith in aerial navigation other than ballooning or of expectation of good results from any of the trials we hear of." ^[52] And in a 1902 newspaper interview he predicted that "No balloon and no aeroplane will ever be practically successful."^[53]

The statement "There is nothing new to be discovered in physics now. All that remains is more and more precise measurement" is given in a number of sources, but without citation. It is reputed to be Kelvin's remark made in an address to the British Association for the Advancement of Science (1900). It is often found quoted without any footnote giving the source.^[54] However, another author reports in a footnote that his search to document the quote failed to find any direct evidence supporting it.^[55] Very similar statements have been attributed to other physicists contemporary to Kelvin.^[56][57]

In 1898, Kelvin predicted that only 400 years of oxygen supply remained on the planet, due to the rate of burning combustibles.^[58][59] In his calculation, Kelvin assumed that photosynthesis was the only source of free oxygen; he did not know about the oxygen cycle.