Whyte notation
File:Locotypes.gif
A selection of early 20th century locomotive types according to their Whyte notation and their comparative size
The Whyte notation for classifying steam locomotives by wheel arrangement was devised by Frederick Methvan Whyte, and came into use in the early twentieth century encouraged by an editorial in American Engineer and Railroad Journal.
Whyte Notation Media
Schematic of 4-2-4 steam locomotive wheel arrangement
Schematic of 0-4-2 steam locomotive wheel arrangement
Schematic of 0-4-4 steam locomotive wheel arrangement