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A recent tome about the history of The Hunt for Vulcan by Thomas Levenson might make your pointy ears wiggle, but the book has nothing to do with Mr. Spock’s home planet. In fact, it’s nonfiction.

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The story began with Urbain Jean Joseph Le Verrier, a “colossus of nineteenth-century science,” who predicted the discovery of Neptune in 1846. What tipped him off? Uranus: its orbit wasn’t quite right according to the Newtonian scheme. Could Newton have been wrong? Or could perhaps Uranus’s abnormalities be accounted for by an unknown mass somewhere out there?

Le Verrier wasn’t the only one to figure this out, by the way: working independently, John Couch Adams was on the same track. But while Adams assumed the solution, Le Verrier established it. The hypothesized new planet would soon be confirmed visually, just as the calculations said it should be. Voilà, Neptune appeared!

And since there was something weird about Mercury, too, Le Verrier thought he could pull off a second planet-discovering coup. Mercury’s slight orbital quirk suggested another gravitational influence other than the Sun. Was there another planet there? In anticipation of its discovery, the hypothetical planet was dubbed Vulcan, after the Roman god of fire and the forge.

Vulcan was never found, of course, although some claimed to have seen it, another interesting example of the phenomenon of wish-fulfillment even among trained observers. Yet Mercury’s wobble was undeniable. So what accounted for it? There seemed to be something more than a Newtonian universe out there. In fact, “almost from Newton’s day, celestial mechanicians had found themselves unable to reconcile theory with observation where Mercury was concerned,” writes J. Donald Fernie. Le Verrier himself cited the “pain and trouble of astronomers” over Mercury.

It wasn’t until 1915, though, with Albert Einstein’s theory of general relativity, that Mercury’s quirkiness could be resolved. Einstein said that space and time were interwoven: the cause of Mercury’s wobble was that the Sun’s massive gravity was distorting space-time before our very eyes.

“Einstein removed the cornerstone [of Newtonianism] altogether and restructured a new celestial mechanics, of which the greatest triumph was the theory of Mercury itself,” writes Norwood Russell Hanson. As Einstein himself said, “the explanation of the shift in Mercury’s perihelion, which is empirically confirmed beyond a doubt, causes me great joy….”

It would have been neat to discover Planet Vulcan, sure, but deciphering a key truth about how the universe works is even neater.


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Isis, Vol. 53, No. 3 (Sep., 1962), pp. 359-378
The University of Chicago Press on behalf of The History of Science Society
American Scientist, Vol. 82, No. 5 (SEPTEMBER-OCTOBER 1994), pp. 412-415
Sigma Xi, The Scientific Research Society