gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1918.018.85.05 On Changing the Plane of a Gnomonic or Stereographic Projection Hilton Harold M.A., D.Sc. Professor of Mathematics in Bedford College (University of London) 8 1918 18 85 244 247 Copyright © 1918, The Mineralogical Society 1918