Background
Clay was born Jacob Claij on January 18, 1882, in Berkhout, Netherlands, the son of Pieter Claij and Neeltje Molenaar. His father was a prosperous farmer.
Wytemaweg 25, 3015 CN Rotterdam, Netherlands
Clay attended Erasmiaans Gymnasium.
Rapenburg 70, 2311 EZ Leiden, Netherlands
Clay studied physics at Leiden University and was assistant to Kamerlingh Onnes from 1903 to 1907. He received his doctorate in 1908.
Clay was born Jacob Claij on January 18, 1882, in Berkhout, Netherlands, the son of Pieter Claij and Neeltje Molenaar. His father was a prosperous farmer.
After attending the Erasmiaans Gymnasium, Clay studied physics at Leiden University and was assistant to Kamerlingh Onnes from 1903 to 1907. He received his doctorate in 1908 with the thesis “De galvanische weerstand van metalen en legeeringen bij läge temperaturen” (“The Galvanic Resistance of Metals and Alloys at Low Temperatures”).
Clay taught in a secondary school at Leiden in 1906 and at Delft from 1907 to 1920. At the Delft Technological University he was privaat-docent in natural philosophy from 1913. In 1920 he became professor of physics at the Bandung Technological University (now in Indonesia) and in 1929 took the same post at the University of Amsterdam.
With interest in general physics and its teaching Clay combined a predilection for philosophy, starting from Hegel, and on the experimental side, for atmospheric electricity. In Bandung, assisted by his physicist wife and his children, he investigated the then rather new subject of cosmic radiation. On voyages from Indonesia to the Netherlands he discovered the latitude effect, a diminution in the intensity of cosmic radiation in the equatorial regions that is caused by the earth’s magnetic field, thus establishing the presence of charged particles in primary cosmic radiation.
Against doubts of other investigators he firmly established the latitude effect and, with the aid of pupils, made further investigations after moving to Amsterdam University. In this connection he worked for the improvement of electric measurements of ionization in general.
Most of his scientific work is published in Physica (The Hague).
Clay’s straightforward nature and honest diplomacy made him a good executive as director of scientific institutions.
Clay's wife was also a physicist, but neither her name nor the date of their marriage are known.