James David Forbes FRS FRSE FGS (20 April 1809 – 31 December 1868) was a Scottish physicist and glaciologist who worked extensively on the conduction of heat and seismology. Forbes was a resident of Edinburgh for most of his life, educated at the University and a professor there from 1833 until he became principal of the United College of St. Andrews in 1859.He invented the seismometer in 1842.