DEGREES KELVIN: A Tale of Genius, Invention and Tragedy
By David Lindley
Aurum, £16.99; 256pp
ISBN 1 845 13000 6
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There are two great errors to which the finest scientific brains are often prone. One is to embrace new thinking so completely that one loses sight of its limits. The other is its mirror image — to hold so inflexibly to the tenets of orthodoxy that one’s mind remains closed to new and better ideas.

For cautionary tales, we have the lives of Francis Galton and William Thomson, Lord Kelvin — the subjects of excellent new biographies. Both shaped the biology and physics of the later 19th century. Yet when they are remembered at all, it is usually for their flaws.

Galton is today the better known of the pair, though the less celebrated during his lifetime. He has become, however, a figure of infamy. He was entranced by the work of his half-cousin, Charles Darwin, and became one of the most enthusiastic promoters of his theory of evolution.

His vision, however, had a darker side. The man who gave us the famous couplet “nature or nuture” was never in much doubt about where he stood on the balance, and founded the pseudoscience of eugenics. Taking Darwin’s ideas to what he saw as their logical conclusion, he suggested that natural selection need no longer control humanity’s destiny.

Instead, it was not only possible but desirable to selectively breed a super-race, by encouraging the fit and intelligent to mate with one another. His theories were to lead to a logical conclusion of their own — the state-sponsored sterilisation programmes of the early 20th century, and Nazi euthanasia.

Galton’s fateful mistake was to abuse theory to justify the prejudices of his age. Modern genetics, indeed, has shown how wrong he was: the Human Genome Project, by revealing the insignificance of differences between ethnic groups, is the ultimate refutation of his racist science.

But as Martin Brookes points out in Extreme Measures, Galton’s contributions to genetics were far from negligible. His was also the captivating life of a genuine polymath. Brookes’s account of his journeys in southern Africa are particularly memorable — not least his measurement of a Hottentot woman’s curves with his sextant.

Kelvin, the first scientist to be raised to the peerage, was the Stephen Hawking of his day — a figure of brilliance and celebrity. As a professor at 22, his work helped the development of the laws of thermodynamics, one of the great breakthroughs of the age. He established the notion of absolute zero, hence the modern temperature scale that bears his name.

Like Galton, Kelvin was a practical man. His advice was vital to the laying of the first transatlantic telegraph cable, and he invented a reliable compass for ironclad ships — tales engagingly narrated by David Lindley in Degrees Kelvin.

Kelvin’s failure was to cling dogmatically to the science of his youth, in the face of new theories with greater explanatory power. Arguing from thermodynamic principles, he insisted that the Earth could be no older than 100 million years — and thus that Darwin’s biology and Lyell’s geology were wrong. He also refused to accept the discovery that explained his mistake — radioactivity. While Kelvin was still revered by the public on his death, he had lost the respect of his peers.

The faults of Galton and Kelvin were certainly not of a piece, but they remind us of an enduring truth about science. Facts are sacred, but tentative: they are the best explanation we have given our current understanding. We assume omniscience at our peril.

Read on

• Newton's Tyranny: The Suppressed Scientific Discoveries of Stephen Gray and John Flamsteed by David and Stephen Clark (W.H. Freeman & Company)
• Huxley: From Devil's Disciple to Evolution's High Priest by Adrian Desmond (Perseus)

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