Rutherford's theory was confirmed in 1932 when experiments performed by the British physicist James Chadwick discovered the neutron, a particle having similar size to a proton but with neutral charge. Shortly after the neutron was discovered the Hungarian physicist Leo Szilard made a theoretical proposal that a nuclear chain reaction could occur as long as neutrons were released as the atoms divided. The groundwork for the Manhattan project had already been started in 1938 by a team of scientists working at Columbia University New York. Slotin held the reflector in his left hand and a long flat ended screwdriver in his right hand, which he used as a wedge to keep the two hemispheres apart. His technique was to rotate the end of the screwdriver to carefully lower the tamper to the point of criticality. This was a tricky operation known as tickling the dragon's tail, a dangerous manipulation that could wake something frightful if it went wrong.