Blaise Pascal, (1623-1662), French mathematician, physicist, inventor and philosopher. At 19, Pascal invented a mechanical calculating engine also known as a pascaline (calculator). It used cogged wheels to perform additions and subtractions, and it is thought that about 70 of them were built. Pascal also made contributions to geometry and hydrostatics. He worked with French mathematician Fermat, founding probability theory. After nearly dying in 1654, Pascal abandoned mathematics in favour of philosophy. The SI unit of pressure, the Pascal, was named after him to honour his work on hydrostatics.