development of a small device to test the mirror configuration. This consisted of a linear pyrex tube with magnets around the outside. The magnets were arranged in two sets, one set of small magnets spaced evenly along the length of the tube, and another pair of much larger magnets at either end. In 1952 they were able to demonstrate that plasma within the tube was confined for much longer times when the mirror magnets at the end were turned on. At the time, he referred to this device as the "pyrotron", but this name did not catch on. Instabilities In a now-famous talk on fusion in 1954, Edward Teller noted that any device with convex magnetic field lines would likely be unstable, a problem today known as the flute instability. The mirror has precisely such a configuration; the magnetic field was highly convex at the ends where the field strength increased. This led to serious concern by Post, but over the next year, his team could find no sign of these problems. In October 1955 he went so far as to state that "it is now becoming clear that in the case of the mirror machine at least these calculations do not apply in detail." In Russia, the first small-scale mirror ("probkotron") was built in 1959 at the Budker Institute of Nuclear Physics in Novosibirsk, Russia. They immediately saw the problem Teller had warned about. This led to something of a mystery, as the US teams under Post continued to lack any evidence of such problems. In 1960, Post and Marshall Rosenbluth published a report "providing evidence for the existence of a stability confined plasma... where the simplest hydromagnetic theory predicts instability." At a meeting on plasma physics in Saltzberg in 1961, the Soviet delegation presented considerable data showing the instability, while the US teams continued to show none. An offhand question by Lev Artsimovich settled the matter; when he asked if the charts being produced from the instruments in the US machines were adjusted for a well-known delay in the output of the detectors being used, it suddenly became clear that the apparent 1 ms stability was, in fact, a 1 ms delay in the measurements. Artsimovich went so far as to claim "we now do not have a single experimental fact indicating long and stable confinement of plasma with hot ions within a simple magnetic mirror geometry." New