Lipsius Building Leiden University, Room 011

Cleveringaplaats 1, Leiden


Boerhaave, Studium Generale

9 May - Jacob Clay’s electrometer: a story of an imperfect discovery

In May 1972, scientist E. M. Bruins wrote a letter to the directors of Museum Boerhaave. In it, Bruins took issue with the bewildering measurements that physicist Jacob Clay had made during sea voyages from Java to the Netherlands from 1927 to 1932. According Clay’s measurements, cosmic radiation decreases in intensity moving towards the equator, a claim that shook the idea of cosmic radiation and the cosmos at its very foundations!

The electrometer that Clay had used to register the intensity of cosmic radiation had previously held a prominent place in the museum. But Bruins believed that Clay had falsified his findings. According to Bruins, Clay’s instruments were not in order and he had deliberately manipulated his data. Was Professor Bruins correct in his suspicions? Had Professor Clay faked his results? In this presentation, Ad Maas reveals the surprising story behind an imperfect discovery. What makes a discovery a true discovery?


Speaker:      Ad Maas, curator at Museum Boerhaave, a specialist in Dutch physics, the history of Dutch science from 1750, Albert Einstein and Dutch Newtonianism. He is also a book review editor for the renowned history of science journal Isis.
Time:          19.30 – 21.00 hours


Please consider that the program of this event is in Dutch