Through Measurement to Knowledge

'Tile; D'apC:Tile; l. DpWTa ()coi 7rpo7rapod)w GBP D'T}K,mi'. 'between us and Goodness the gods have placed the sweat of our brows'. This quote from Isiodos, the first lyrical poet, is jotted on a sheet of paper found among the papers of Heike Kamerlingh Onnes at the Boerhaave Museum, Leiden. On this same sheet, one can also read quotes from Schiller, Goethe, Shakespeare, Homer, Pindar and Dante. Each quote is for somebody or something. It appears to have been a game played at least by Ehrenfest and Crommelin -an unmistakable sign of these two physicists's deep culture. This particular quote was for the 'Werkplaats', the Physical Laboratory of the University of Leiden. Our purpose in putting together the Selected Papers of its first Director, Kamerlingh Onnes (1853-1926), is to try and articulate the dominant trends of a different type of culture at Leiden: its physics culture during the years that established low temperature physics as a distinct branch of physics. Our aims in choosing the particular papers are threefold. First, we wish to present the interconnectedness among the different research programs of Kamerlingh Onnes and to bring out the decisive role of the work initiated by van der Waals in determining the direction of nearly all of these research programs.