For as long as the name Einstein is remembered, it will surely be as a conjurer of great ideas, relativity being foremost among them. But the most celebrated theoretical physicist of all time also tried his hand once at designing an experimental instrument. It didn't amount to much, but that doesn't make it any less fascinating to physicists, who have now reconstructed the device that Einstein called his "little machine."

In his biography of Einstein, the late physicist Abraham Pais asserted that the old man's biggest gift lay in an unprecedented understanding of statistical phenomena, which, for one thing, allowed Einstein to prove the existence of atoms by analyzing the zigzag Brownian motion of particles in water. Two years after that breakthrough, in 1907, Einstein applied a similar statistical perspective to electrons in a capacitor, a simple device for storing electrical charge, says physicist Danny Segers, director of the Museum for the History of Sciences in Ghent, Belgium. Einstein reasoned that when a capacitor is allowed to discharge, it should still contain a small voltage in the vicinity of one half millivolt. Today a voltmeter from the hardware store will tick off fractions of millivolts, but a century ago it was impossible to measure voltages that small, Segers explains.

So from 1907 to 1910 Einstein worked on a design he devised for amplifying a voltage--his Maschinchen, or little machine, as he would later refer to it. His friends Paul Habicht, an engineer and instrument maker, and Paul's brother Conrad helped him perfect the device, three copies of which survive in museums.

"When you look through the literature you don't find any measurements done on it, so we had doubts whether the machine ever worked," Segers says. Wanting to test one directly, Segers and his colleague Jos Uyttenhove built their own Maschinchen, based on a schematic published by the Habichts and an interior view of one of the museum pieces. They assembled a stack of six stages, or groups of metal plates, housed in a cylinder. In the first stage a plate slides past the discharged test capacitor, picking up a charge induced by any residual voltage left in the capacitor, and deposits this amplified charge in the next stage, where the process repeats to create a measurable signal.

Although the device works, the reconstruction confirms that Einstein made the right choice in remaining a theorist. The charge accumulated in the instrument fluctuates by a small amount, probably because of its mechanical contacts. This variability likely renders it too imprecise for the measurements Einstein desired, reports Segers, whose admiration for the great physicist is undiminished. "The amazing thing for me as a physicist is I did not know Einstein was interested in experimental work," he says. "I'm not going to say Einstein used a screwdriver himself, but he certainly understood very well how things worked."