Engines of Our Ingenuity

No. 2269:
JAMES DAVID FORBES

by John H. Lienhard

Today, a story of heat and ice. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

James David Forbes was born in Edinburgh in 1809. His mother died during his infancy, and his father (a baronet and a banker) hired a private tutor to educate him at home. Forbes grew up, according to one biographer, conservative, superior, and aloof.

But let's not give up on him yet: He went on to the University of Edinburgh. There he won academic prizes and began writing articles on meteorology. The articles got him into the Royal Society of London, though he had to wait 'til he became 21. Next, through political machinations, he became a professor at Edinburgh. Still, he did well, the great James Clark Maxwell was one of his students.

Forbes' real scientific work lay ahead; and we might divide it into heat and cold. His work on heat was well-received, but with a rather cool detachment. His work on cold glaciers, on the other hand would result in a furnace blast of emotional heat.

First, heat: Italian scientist Macedonio Melloni had found that infra-red heat radiation refracts the way light does. With Melloni's help, Forbes went on to find that heat radiation, like light, can also be polarized. Heat, it seems, behaves just the way light does, only humans can't see it. He also measured the temperature gradient in Earth's surface. Lord Kelvin later used those data to estimate Earth's age as a hundred million years -- a number far too low for geologists and far too high for fundamentalists.

But we learn none of that from Forbes' thick biography. It came outfive years after he'd died (probably of TB) at the age of 59, and it only briefly mentions his work on heat. It deals mainly with his work on cold glaciers.

Forbes was among the first to recognize that glaciers move like very viscous liquids, even though they're made of brittle ice. At first, Forbes didn't say how they did; but another scientist, John Tyndall, said that glacial ice constantly breaks up, then freezes back together -- creating an illusion of fluid motion.

Forbes did not like that, so he and Tyndall were soon at it. Then Louis Agassiz, who'd taken Forbes to the Aar Glacier, ' accused him of stealing his ideas. Animosity spread. And Forbes is mainly remembered for a great scientific cat fight. He didn't help matters when in later life he became greedy for academic power and honor.

And yet, Forbes' work with heat radiation was a first step on the way to Max Plank setting the basis of quantum physics. And the viscoplastic movement of glaciers is like the movement within Earth's mantle. Kelvin's estimate of Earth's age, based on Forbes' data, was defeated by those glacial movements below Earth's surface. Forbes' work continued to echo in so much that followed it.

Well, I suppose we all misjudge our own doings even more grievously than we misjudge others. Forbes died without realizing that he'd made greater contributions in his cool studies of heat, than he ever did in his overheated studies of ice.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)


J. C. Shairp, P. G. Tait, A. A. Reilly, Life and Letters of James David Forbes, F.R.S. (London: Macmillan and Co. 1873) (Both images are from this source.)

J. G. Burke, Forbes, James David. C. C. Gillispie, ed., Dictionary of Scientific Biography, Vol. V (New York: Charles Scribner's Sons, 1972).

R. N. Smart, Forbes, James David (1809-1868), Oxford Dictionary of National Biography, Vol. 20, (Oxford: Oxford University Press, 2004): pp. 364-397.

James David Forbes

For Forbes' detailed drawing of the glacier at Mt. Chamonix, click on the image below:


The Engines of Our Ingenuity is Copyright © 1988-2006 by John H. Lienhard.