The elder son of Major Alexander Kenneth Hope Johnston, a British Army officer, and his wife Lydia Lutener,[1] Johnston was born at Aldershot and educated in Valletta, Malta, at Edinburgh University, where he graduated MA in mathematics and natural philosophy, and then finally at Pembroke College, Cambridge, graduating BA in 1897 in the mathematical tripos as 14th wrangler.
[3] After leaving Cambridge, in 1898 Johnston was appointed as "professor" of physics at the Royal Agricultural College, Cirencester, but stayed for only one year.
Under his headship, science fifth and sixth forms were created, in which the main subjects were chemistry, physics, biology, and astronomy.
He acquired a Sopwith Snipe aeroplane and five engines for it, and an Avro 504K biplane, which was housed in a hangar on top of the new Science Building, for the boys to work on.
[5] Their younger son John Alexander Hope Johnston became a pilot officer in the Royal Air Force and was killed on 18 April 1941, aged 27, on active service during the Second World War.