A photograph hangs in the stairwell of the east wing of Caltech’s Norman Bridge Laboratory of Physics. Dating from 1922, it depicts 25 professors and students posing in their Sunday best with a dog lying at their feet (see figure 1). They are there to attend a special lecture series on light and matter. Seated in the middle of the front row, to the right of laboratory director Robert Millikan, sits the lecturer: Hendrik Lorentz, a theoretical physicist from Leiden University in the Netherlands.
Millikan and Lorentz are celebrated for their tremendous contributions to early-20th-century physics. But they also made their mark in the realm of international science policy. Based on the archives of Millikan and Lorentz in Pasadena, California, and Haarlem, the Netherlands, respectively, this article reconstructs a little-known aspect of that work: their joint effort to restore scientific cooperation between countries that had fought hard to destroy...
