At the other end of the scale, one-cylinder locomotives have been extremely rare, for excellent reasons. A machine with one cylinder on one side would be horribly unbalanced, and there would be the problem of the loco stopping on a dead centre. (ie with the crank at either the three o'clock or nine o'clock position, so that the piston thrust gave no rotational effect)
Nevertheless, here is such a locomotive. Built by Nielson (a name we have noted before in these pages) in 1857, It was a an 0-4-0 saddle tank with a single cylinder (10" x 16") mounted under the firebox and footplate, driving a horizontal equalising beam that moved in the slots seen at the rear.
A number of these were built for shunting in the collieries and ironworks of Scotland.
Left: The Nielson One-Cylinder Locomotive.
74 fire tubes 5' long.