1851 Great Exhibition: Official Catalogue: Class IX.: George Robertson
From Graces Guide
26.,ROBERTSON, GEORGE, Allardice Street, Stonehaven, Scotland — Inventor.
One-horse cart for agricultural purposes; with a sliding axle, by which the weight on the horse's back is regulated in going up or down hill; it has the advantage of keeping the cart always on a level. This invention is intended to prevent horses being at one time crushed with too much weight, and choked at another with too little.