Johnson, J
Chief Mechanical Engineer for the Great North of Scotland Railway from 1890
to 1894.
Johnson, S.W
Chief Mechanical Engineer for the Great Eastern Railway from 1866 to 1873,
also for the Midland Railway from 1873 to 1903.
Journal
That part of an axle which rotates inside an axlebox and thus forms
the bearing surface.
Joy valve-gear
A type of locomotive valve-gear, where the movement is derived from
a vertical link connected to the connecting rod. The vertical
movement is translated into the horizontal movement required by the
valve spindle by a die block moving in a slide which can be
varied in inclination.