The birth of liquid helium took place in Leiden some 75 years ago on 9 July 1908. After that initial liquefaction, by Kamerlingh onnes, there followed three decades during which the liquid was employed chiefly in a subservient role, as a coolant for experiments on other materials at very low temperatures. Astonishingly, its superfluid properties had simply passed unnoticed. This remarkable state of affairs should probably be attributed more to the extraordinary nature of liquid 4He itself than to any dilatoriness or lack of imagination on the part of the investigators; for superfluid helium is utterly different to any physical system studied prior to 1908. Even today, although enormous progress has been made, the liquid remains in many ways an enigma and it continues to be the subject of intense experimental and theoretical investigation.
Report on the international conference to mark the 75th anniversary of the original liquefaction of helium in Leiden On 9 July 1908. The Jubilee Conference was organised in St Andrews by J.F. Allen, a co-discoverer of superfluidity in liquid 4He, 1-5 August 1983.