File talk:Roberts tracked steam tractor.jpg

This picture is not of the (only) Hornsby steam powered chain tractor: built-to commercial order for the Northern Light and Power Company in 1909/1910. That machine, the Hornsby Mammoth, had/has only two carrying wheels each side, whereas this picture shows a tractor with three. The Mammoth was in essence an over-type traction engine on a crawler track chassis. Photographs of the machine show the boiler was high pitched and the crankshaft carried a single disc flywheel. This photograph, indicates a low pitched crankshaft and two flywheels are evident, one of which on the RHS of the machine appears to have curved spokes. The chimney- which to modern eyes suggests a steam engine is a red herring- early paraffin engined tractors were sometimes fitted with funnels similar to a steam traction engine. This may have been partly convention, but was also functional in the case of engines in which water cooling was by evaporation, as they provided a safe (and conventionally obvious) high-level discharge for the resulting waste steam.

I suggest the photograph actually shows one of the earlier Hornsby chain tractors, built as demonstration machines. At least one of these is reported to have had a paraffin oil engine, water cooled by evaporation. Donnghaileach (talk) 20:15, 8 December 2013 (UTC)