Stjepan Mohorovicic (1880-1980), professor of physics at a grammar school in Zagreb, made a very important theoretical discovery of the positronium (rotational pair of electron and positron) as early as in 1934, published in “Astronomishe Nachrichten”, a prestigeous German scientific journal (precise reference is A. Mohorovicic, Astron. Nachr. 253, 94 (1934)). Its existence was confirmed experimentally in 1951 by Martin Deutsch, MIT physicist (and a member of Manhattan Project). 

Still earlier, in 1927, Stjepan Mohorovicic predicted the existence of the MOHO-layer on the Moon, analogous to that of the Earth, discovered by his father Andrija Mohorovicic. Its existence has been proved in 1969 during the famous Apollo 11 flight to the Moon. Seismic measurements have been carried out by Neil Armstrong and Edwin Aldrin, the first humans to land on the Moon.

Stjepan Mohorovicic with his father Andrija Mohorovicic.