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No. 857:
Tyndall on Parallel Roads

Today, we ask why three roads should run parallel to each other. 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.

In 1854 the Irish physicist John Tyndall lectured on science education in London. Science he said, begins with a question. To answer a question about nature, we must first observe. We must take in sense data -- heat, light, sound. But, he continues,

we observe the fact, but are not satisfied with observation: the fact must be accounted for ... we transfer [facts] to the domain of thought: look at them, compare them, [bring] them ever clearer before the mental eye. [And finally we] alight upon the cause which unites them.

Tyndall came back to that elemental theme again and again. We must move back and forth between an observed world and an invented world. It is never enough to observe. It is never enough to theorize. We must do both, or we accomplish nothing.

Then, 22 years later, Tyndall gave another lecture. This time he talked about the mysterious parallel roads of Glen Roy.

Glen Roy is the valley of the River Roy in Scotland. High on either side, three parallel roads wind along the canyon wall -- only a stone's throw apart.

Tyndall had found a question, all right. Those remote improbable roads were there long before any account of them. But, for the last hundred years, people had been asking why three roads should be made parallel to one another. He says,

[We need] two distinct mental processes [to treat] such a question. [First,] faithful observation of the data; [second,] that higher mental process in which the constructive imagination comes into play, connecting separate facts with their common cause, and weaving them into an organic whole.

Tyndall asks us to begin with detached observation. Then we undertake the very personal process of inventing a theory.

Scottish country folk had done that. They explained those crazy roads by saying their ancestors had made them as open areas to tempt game out of the brush and into a vulnerable position.

Then the scientists came. They said, Wait a minute! Those aren't roads at all. They're terraces formed by water levels in the valley. That's why their elevation doesn't vary. But how did the valley fill with water for long periods and then empty out?

They finally saw how subsequent glaciers had dammed the outlet of the valley. By the time they had it right, the great minds of the age had wrestled with those mad roads that weren't roads at all -- Charles Darwin, Louis Agassiz, and Tyndall, too.

Tyndall didn't really care about the answer -- even though he'd helped to find it. He wanted us to know the process that begins with a small question about three crazy roads and ends with a new understanding of geology. What held Tyndall's heart was the joy of marrying the mind to external data. That essential act of science is laid bare in our response to a question about eerie roads that weren't at all what they seemed to be.

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

(Theme music)

Tyndall, J., Fragments of Science. Vol. I, 6th ed., New York: D. Appleton and Co., 1899, Chapter VIII, The Parallel Roads of Glen Roy.

Tyndall's first written reference to the parallel roads of Glen Roy was Pennant, T, A Tour in Scotland. Vol. iii, 1776, p. 394.

For more on Tyndall see Episodes 192531624642, and 1067. The Tyndall quotations have been edited down for use on the radio. See the source for complete quotations. Much additional material on Tyndall and on the observations of many Scottish naturalists is available in Special Collections, UH Library.


The parallel roads of Glen Roy (from Fragments of Science, 1899)
Image courtesy of Special Collections, UH Library

The parallel roads of Glen Roy (from Fragments of Science, 1899)


John Tyndall, from the frontispiece of his book, Forms of Water in Clouds and Rivers, Ice and Glaciers, 1874
Image courtesy of Special Collections, UH Library

John Tyndall, from the frontispiece of his book, Forms of Water in Clouds and Rivers, Ice and Glaciers, 1874