Jacob Clay (18.01.1882 - 31.05.1955) was a Dutch physicist. He was born in Berkhout. He studied at the University of Leiden, where in 1903 — 07 he was an assistant to H. Kamerlingh Onnes, and in 1908 he received the degree of Doctor of Philosophy. In 1907 — 20 he worked at the Higher Technical School in Delft, from 1920 he was professor at Bandung University (Indonesia) and from 1929 at Amsterdam.
A pioneer in the study of cosmic rays. Independently of A. Compton he discovered (1927) variations in the intensity of cosmic rays with latitude (the latitude effect). His research also concerned the improvement of electrical measurements of ionisation.