Rotary Snow Plough

Jull claims cutting-blades that slice snow from the bank and fan-blades that throw it clear, operating on a common centre. Write both down as separate jobs.

Fold a card wedge about 100 mm wide and glue it to the front of a small card truck. This is the machine Jull was trying to beat.

Heap plain flour across a tray to make a bank about 50 mm deep, and pat it down firmly. Loose flour is fresh snow; packed flour is the drift that stops trains.

Run the wedge at the bank at a fixed speed. Measure how far it penetrates before it stalls and piles up. Record it.

Cut a 90 mm card disc and glue on four rectangular vanes, standing square to the disc, evenly spaced. This wheel only throws.

Cut a second 100 mm disc, cut four angled slots in its rim and bend the flaps forward into cutting edges. This ring only slices.

Push a dowel through both discs, knife ring in front, fan behind, about 20 mm apart. Both turn together on a common centre, as claimed.

Wrap a card cylinder round the wheels, open at the front, with a chute cut in one side. Bearings: two holes in card end-plates for the shaft.

Bend a wire crank onto the shaft. The plough now has power of its own, independent of how fast it is pushed forward. That is the difference from the wedge.

Crank steadily and advance the plough slowly into the packed bank. It cuts in and throws a stream of flour out of the chute. Measure the penetration and compare with step 4.

Crank slowly, then fast. Measure how far the flour lands each time. Throw distance climbs steeply with rim speed — centrifugal force, not shovelling.

Run the fan alone into packed flour. It rubs and stalls — a fan cannot cut. Refit the ring: it bites again. The two jobs really are separate.

Cut a second chute on the other side and block one at a time. A real rotary must be able to throw downwind and away from the line, or it buries the track it just cleared.

The patent. US 297,408, "Snow plow", granted 22 April 1884 to Orange Jull. The specification describes cutting-blades that slice the snow from the bank and fan-blades that throw it clear by centrifugal force, working on a common centre, and notes the mechanism may be driven by an independent steam-engine. Jull is explicit that it is intended for railroads but could clear highways or work as an excavator.

Why the wedge had to go. A wedge plough converts the train's kinetic energy into snow displacement. That energy is fixed by the locomotive's speed and mass, so against a deep packed drift the train decelerates, the snow compacts ahead of it, and the plough stops — often stuck fast (step 4). A rotary brings its own engine, so the power going into the snow does not depend on forward speed at all. It can crawl forward at walking pace and still cut at full force (steps 9-10). This is a general engineering lesson worth keeping: when momentum is not enough, stop trying to go faster and drive the working element directly.

Why two blade sets. Packed snow must first be broken loose, then moved. A fan alone polishes and jams against a hard face (step 12); knives alone would loosen snow with nowhere to send it. Separating the functions and putting them on one shaft means one engine does both, and each set can be shaped for its own job — sharp angled edges for cutting, flat radial vanes for throwing. Throw distance rises sharply with rim speed (step 11), which is why rotaries can hurl snow far clear of the formation instead of piling it beside the rails to drift back.

Who built it. Jull, of Orangeville, Ontario, obtained patents in 1884 and assigned the rights to John and Edward Leslie, who developed and manufactured the machine — the first was built in 1885, and the Leslies formed a company to produce them. The rotary was decisive on mountain lines: crossings like Donner Pass in the Sierra Nevada became workable in winter in a way they had not been before. Jull himself went on to a different design, a screw-type "Jull centrifugal excavator", which was not the one that lasted.

An earlier idea that was never built. The rotary concept had been proposed years before by a Toronto dentist, J. W. Elliot, who patented a revolving snow shovel in 1869 but never constructed one. It is a familiar pattern in this programme: the person who first has the idea and the person who makes it work are often not the same, and the patent record shows both. Jull's contribution was a design that could actually be built and driven.

Where it sits. Rotary ploughs still clear mountain railways and airport runways, now diesel or electric rather than steam, and the domestic snow blower in a suburban garage is the same machine shrunk — an auger to cut, an impeller to throw, and a chute you aim downwind.