Side view depiction of a <a href="https://en.wikipedia.org/wiki/Norris_Locomotive_Works" class="extiw" title="w:Norris Locomotive Works">Norris</a> <a href="https://en.wikipedia.org/wiki/4-2-0" class="extiw" title="w:4-2-0">4-2-0</a> locomotive of 1840.
S. M. Vauclain
S. M. Vauclain, "Outline History of Locomotive Development", <a rel="nofollow" class="external text" href="https://archive.org/details/railwaylocomotiv36newyuoft/page/227">p. 227</a>, in <i>Railway and Locomotive Engineering</i>, vol. XXXVI, no. 7, July 1923.