Prof James Gordon MacGregor, FRS FRSE LLD (31 March 1852 in Halifax, Canada – 21 May 1913 in Edinburgh) was a Canadian physicist. He was described as "brilliant, energetic, nervous, impatient", and not suffering fools gladly.
He was born in Halifax in Nova Scotia on 31 March 1852, the son of Rev Peter Gordon MacGregor DD. He was educated there at the Free Church Academy then studied at Dalhousie University where he graduated MA. He then left Nova Scotia and did postgraduate studies at Edinburgh University, the University of Leipzig and the University of London.
He returned to Nova Scotia to lecture in Physics at his alma mater, Dalhousie University, for one academic year, 1876/1877. In the summer of 1877 he relocated to England to serve as Science Master at Clifton College in Bristol. In 1879 he returned to Dalhousie as a Professor of Physics and stayed in this role for 21 years.
He clearly retained links to Britain as in 1880 he was elected an Ordinary Fellow (rather than Foreign Fellow or Honorary Fellow) of the Royal Society of Edinburgh. His proposers were Peter Guthrie Tait, Alexander Crum Brown, John Hutton Balfour and Edmund Albert Letts. In 1900 he was also elected a Fellow of the Royal Society of London.