The tractor

A tractor is an engine you can drive to the work and hitch to anything. On a strong frame sit the engine, a gearbox giving forward and reverse, and large driving wheels for grip on soft ground; at the back a drawbar pulls implements — plow, harrow, planter, wagon — and a belt pulley (later a spinning power take-off shaft) sends the engine's power to machines that stand still, like a thresher or a baler. The decisive early feature was not the engine alone but the gearing that let the machine propel and reverse itself reliably. A stationary engine on wheels that cannot back out of a corner is of little use in a field; a machine that can crawl forward, stop, and reverse under its own power is a tractor.

Steam traction engines already existed and could pull plows, but they were monsters to keep: several tons of iron, a boiler that took an hour to raise steam, and a constant appetite for coal or wood and for water that had to be hauled to them across the field. Their fireboxes threw sparks into dry stubble, a real risk of burning the very crop being worked. A gasoline tractor started cold, carried its energy as a tankful of liquid, weighed far less, and lit no fire in the open. And by replacing the horse it freed the enormous acreage that horses themselves consumed — a large fraction of a farm's land had grown the oats and hay to feed its draft animals. Every acre no longer feeding horses could now feed people.

The tractor mechanized the farm and retired the horse. In the United States the working-horse population peaked around the First World War and then fell away as tractors spread; Henry Ford's mass-produced Fordson (1917) put them within reach of ordinary farmers. Coupled to ever-larger plows, planters, and combines, the tractor let a shrinking number of farmers work an expanding acreage, which pushed farm labor into the cities and underwrote the century's growth in food output. The line Froelich started, absorbed into John Deere in 1918, remains one of the largest tractor makers in the world.