Sir Harold Jeffreys, noted British astronomer and geophysicist, was born on this day in 1891. Jeffreys investigated the thermal history of Earth and was the first to propose that Earth's core is liquid. He also co-authored the standard tables of travel times for earthquake waves published in 1940, explained how monsoons and sea breezes arise, and recognized the importance of cyclones in the general circulation of the atmosphere.
Jeffreys devised models of the internal structure of the four large outer planets--Jupiter, Saturn, Uranus, and Neptune--and determined that they were very cold. He was knighted in 1953 and died in 1989.
[Source: Britannica Online]