Kamerlingh Onnes’ talents for solving scientific problems was already apparent in 1871, when at the age of 18 he was awarded a Gold Medal for a competition sponsored by the Natural Sciences Faculty of the University of Utrecht, followed the next year by a Silver Medal for a similar event at the University of Groningen. When working with Kirchhoff he also won the “Seminarpreis”, entitling him to occupy one of the two existing assistantships under Kirchhoff.

In his doctor’s thesis theoretical as well as experimental proof was given that Foucault’s well-known pendulum experiment should be considered as a special case of a large group of phenomena which in a much simpler fashion can be used to prove the rotational movement of the earth. In 1881 he published a paper Algemeene theorie der vloeistoffen (General theory of liquids), which dealt with the kinetic theory of the liquid state, approaching Van der Waals’ law of corresponding states from a mechanistic point of view. This work can be considered as the beginning of his life-long investigations into the properties of matter at low temperatures. In his inaugural address De beteekenis van het quantitatief onderzoek in de natnurkunde (The importance of quantitative research in physics) he arrived at his well-known motto “Door meten tot weten” (Knowledge through measurement), an appreciation of the value of measurements which concerned him throughout his scientific career.

After his appointment to the Physics Chair at Leyden, Kamerlingh Onnes reorganized the Physical Laboratory (now known as the Kamerlingh Onnes Laboratory) in a way to suit his own programme. His researches were mainly based on the theories of his two great compatriots J.D. van der Waals and H.A. Lorentz. In particular he had in mind the establishment of a cryogenic laboratory which would enable him to verify Van der Waals’ law of corresponding states over a large range of temperatures. His efforts to reach extremely low temperatures culminated in the liquefaction of helium in 1908. Bringing the temperature of the helium down to 0,9°K, he reached the nearest approach to absolute zero then achieved, thus justifying the saying that the coldest spot on earth was situated at Leyden. It was on account of these low-temperature studies that he was awarded the Nobel Prize. Later, his pupils W.H. Keesom and W.J. de Haas ( Lorentz’ son-in-law) conducted experiments in the same laboratory which led them still closer to absolute zero.

Other investigations in his laboratory which gradually gained in importance and international fame, included thermodynamics, the radioactivity law, and observations on optical, magnetic and electrical phenomena, such as the study of fluorescence and phosphorescence, the magnetic rotation of the polarization plane, absorption spectra of crystals in the magnetic field; also the Hall effect, dielectric constants, and especially the resistance of metals. A momentous discovery (1911) was that of the superconductivity of pure metals such as mercury, tin and lead at very low temperatures, and following from this the observation of persisting currents.

The results of Kamerlingh Onnes’ investigations were published in the Proceedings of the Royal Academy of Sciences of Amsterdam and also in the Communications from the Physical Laboratory at Leyden. Many foreign scientists came to Leyden to work in his laboratory for shorter or longer periods. The laboratory gained additional fame throughout the world through the training school for instrument-makers and glass-blowers housed in it, founded by Kamerlingh Onnes in 1901.

At the early age of 30, Kamerlingh Onnes was appointed a member of the Royal Academy of Sciences of Amsterdam. He was one of the founders of the Association (now Institut) International du Froid. He was a Commander in the Order of the Netherlands Lion, the Order of Orange-Nassau of the Netherlands, the Order of St. Olaf of Norway, and the Order of Polonia Restituta of Poland. He held an honorary doctorate of the University of Berlin, and was awarded the Matteucci Medal, the Rumford Medal, the Baumgarten Preis and the Franklin Medal. He was Member of the Society of Friends of Science in Moscow, and of the Academies of Sciences in Copenhagen, Uppsala, Turin, Vienna, Göttingen and Halle; Foreign Associate of the Académie des Sciences of Paris; Foreign Member of the Accademia dei Lincei of Rome and the Royal Society of London; and Honorary Member of the Physical Society of Stockholm, the Société Helvétique des Sciences Naturelles, the Royal Institution of London, the Sociedad Española da Física y Qumica of Madrid, and the Franklin Institute of Philadelphia.

Outside his scientific work, Kamerlingh Onnes’ favourite recreations were his family life and helpfulness to those who needed it. Although his work was his hobby, he was far from being a pompous scholar. A man of great personal charm and philanthropic humanity, he was very active during and after the First World War in smoothing out political differences between scientists and in succouring starving children in countries suffering from food shortage. In 1887 he married Maria Adriana Wilhelmina Elisabeth Bijleveld, who was a great help to him in these activities and who created a home widely known for its hospitality. They had one son, Albert, who became a high-ranking civil servant at The Hague.