By Roland Pease
BBC radio science
If nanotechnology - engineering at close to the molecular scale - sometimes seems like a religion, complete with competing sects and prophets, then its old testament is a talk given in 1959 by the celebrated American scientist Richard Feynman.
The large blob is a pinhead; McLellan's motor is smaller still (Image: Caltech Archives>)
Entitled There's Plenty Of Room At The Bottom, the talk looked forward to an age when the pages of books could be reduced to collections of dots composed of a few atoms, and computer circuits could be made from wires a thousand times narrower than a human hair.
The first shrine, then, is a display just outside Feynman's old office at the California Institute of Technology, of an electric motor no bigger than a grain of salt, made in response to a challenge by Feynman at the end of his talk.
And it was during a lull in recording for Small Worlds - BBC Radio 4's new series on nanotechnology - that we happened to meet the man who made the motor, by hand, 44 years ago.
Bill McLellan had seen a copy of Feynman's talk in Engineering And Science, Caltech's internal magazine.
He did not do anything at first, but by June 1960 he realised no else had managed it.
21st-Century nanomotors use new carbon technologies to achieve much finer scales (Image: Alex Zettl)
"I knew how to make it, and I wondered why nobody did. Of course once I got into it I realised why - they were smart and it was too much work." Five months' work, in fact, done over lunchtime with two colleagues at the scientific instrument makers he worked for.
Richard Feynman had specified a working electric motor no more than 1/64th of an inch on a side, confidently expecting making such a device would take an entirely new approach to engineering. Bill McLellan proved him wrong.
"He'd seen a lot of cranks come in with motors who didn't understand the challenge and I brought in a big box, and he said 'Uh-oh, here's another one of them'. And then I opened my wooden box and there was my microscope, and he said 'Oh! Nobody else brought a microscope!'".
But Feynman had to agree, the motor met his specification.
"It's actually fourteen thousandths of an inch on a side - a 64th is 15.6 thousandths, but I wanted to be sure that there wasn't a wire hanging over. It's just like a pencil dot, that's all it is."
Although McLellan made the motor by hand, so subverting Feynman's intent, among his tools was a sharpened toothpick which pushed the Lilliputian components into place - appropriately presaging the atom-fine tips of atomic-force microscopes which nanotechnologists use today for their molecular construction kits.
To make the wires for the motor, McLellan took the finest he could find, and then rolled it between two glass microscope slides until he got the width he needed - about the width of a hair. To get the central rotor on to its shaft, he picked it up between the hairs of the finest artist's paint brush around.
Feynman liked what he saw and offered up the prize money (Image: Caltech Archives>)
McLellan made 10 motors in all - none works now. The one on display at Caltech finally failed in 1991. A BBC cameraman crushed another one, according to McLellan, trying to get a better focus on it.
"Feynman's disappointment was he didn't get the new method," says McLellan.
Nevertheless, he handed over the $1,000 prize he had promised. And McLellan said it did help Feynman's goal in the longer term.
"Kids would write and say, 'I'm going into miniaturisation'. So it inspired people, even though it didn't produce what Feynman wanted, the result got everyone interested in it. It sure stirred up interest, so I think it was a good thing."
Small Worlds is a new three-part series that begins on BBC Radio 4 on Wednesday, 9 June, at 2100 BST