THE mountains at Buchs, near St Gallen in north-east Switzerland, rise to more than 2,200 metres, with Buchs itself clustered under a long rampart of peaks. A boy brought up on a farm here, as Heinrich Rohrer was, coping with cows on one steep incline after another, naturally thought about the lie of the land. It was natural, too, not to feel intimidated by the mountains. If they could not be climbed over - and he was always an avid hiker, rather than a mountaineer - then they could usually be tunnelled through to get to the other side. In a typically Swiss way, he liked tunnels. Small wonder, then, that when he accidentally fell as a young man into the world of physics, he came to specialise in superconductivity, or the flow of electricity without resistance through materials at very low temperatures. Having exhausted his interest in that, he began to think about tunnelling from one atom to another, as if the vacuum between them were as dense and difficult as a mountain. In 1981, working at the IBM Research Laboratory near Zurich, he and his colleague Gerd Binnig discovered that such "quantum tunnelling" could be done with a moving probe sharpened to a single atom at the tip. They called it the Scanning Tunnelling Microscope (STM). When a voltage was applied to the tip, electrons leaked across the small vacuum gap that separated the tip from the surface it was hovering over. This seemed impossible; but, under the laws of quantum mechanics, a fundamental uncertainty in the energy of each electron meant that, for one instant, it was able to break through the barrier. As the tip scanned back and forth, differences in the tunnelling current also showed up measurable variations in the atomic surface, revealing not only what atoms looked like but also what they might feel like, if you could glide your fingers across the bumps. "Topography" was not quite the right word, since the STM was tracking electrical properties. But it gave each crystal surface a distinctive landscape, which to Dr Rohrer's joy often looked rather like the Alps. With the right colour-coding of the STM trace of the surface of graphite, "land" rose out of blue lakes to become green hills, merging to brown, and then to snow-capped peaks. When in the late 1980s the STM was integrated with a computer (the two technologies fortuitously appearing at the same time), the 3D images became dazzling. Carbon atoms clung together "very nicely" in a honeycomb lattice. A crystal of gold made an arrangement of broad atomic terraces. A surface of silicon was revealed as a land of gentle, steadily rising undulations, in which the track of the probe could be seen like furrows dug with a plough. This particular image was so riveting and so beautiful that "Heini" (as Dr Rohrer told everyone to call him) had to take young Dr Binnig away for long walks through the real mountains to get their discovery in perspective, and to calm him down. Working at the nano scale, one-billionth of a metre, the STM did not merely touch atoms. It could also nudge them around, offering the prospect of building with them, as only Nature had done before. The first attempt, by Don Eigler in 1989, spelled out "IBM" with 35 xenon atoms. Eager Utopians predicted that nanotechnology would one day lead to a "universal assembler," enabling scientists to build from the atomic level everything from cabbages to cars to human beings. Less than Columbus Dr Rohrer, ever down-to-earth, did not think he and Dr Binnig had triggered a revolution: certainly not one to compare with the industrial revolution, or even with the voyages of Columbus. You see, he would say in his sing-song accent, "just getting smaller alone does not make a revolution." What pleased him most about the STM project, apart from the results, was its simplicity and their own free, lighthearted approach to it, just tinkering with it on the side while doing other work for IBM. They had built the first STM on a shoestring budget, which satisfied his frugal mind: it was held together with Scotch tape, and operated (to reduce vibration) only at night, in breath-held silence. No wild expectations, no big promises. But the gadget worked. Many other scientists had said it never could. They mocked the project, not least because Dr Rohrer and Dr Binnig had no background either in surface science or in microscopy. Believers in the STM were hard to find at first. But in 1986, when the pair received the Nobel prize for physics, it took its rightful place as chief pathfinder through the new nano-worlds. Dr Rohrer still considered himself, with delight, as a neophyte in that field. It was something of a habit. He had known almost nothing of physics when he enrolled, at 18, in the Swiss Federal Institute of Technology; and he was still being taught the subject, he wrote, by "so many patient colleagues" at IBM for the 34 years he was there. But that was a good thing. Because he thought himself no expert, he could bring to his work fresh, unbiased eyes, like those of the students whose company, over a beer or two, he so enjoyed. Like them, he did not think of obstacles, or feel the burden of fame. When asked if the Nobel prize had changed him, he said simply, "All in all, I think I did not lose the ground under my feet."