In the first half of the 1800s, getting from one side of the United States to the other was a significant affair. There were no planes back then (of course), no cars, and the overland route via covered wagon was even more treacherous than the video games of our youth alluded to. In 1863, workers broke ground on the US transcontinental railroad. By 1869, one could ride from Nebraska to California in a week, instead of the six treacherous months previously required. It was one of the most remarkable feats of civil engineering – not to mention sheer labor – of the 19th century. Not only did the railroad unite the country with transportation, it also enabled a new era of communication: telegraph lines were installed next to the railroad, allowing messages to be sent instantly across the country.

One can imagine the number of calculations required to build a single trestle, let alone an entire 1780 miles of railroad. Only about 25% of the workers involved in the project were actually physical laborers doing the blasting, digging, and other heavy work. It is some of the other workers who would have most benefited from access to a difference engine.

For one, there is the obvious need for engineers to perform calculations regarding where it is most efficient to lay the route, how strong bridges must be to support the trains, how far it can be between refueling points without trains running out of coal and other supplies, and countless other mathematical problems. Indeed, any engineering project in that era would have benefited greatly from access to more accurate and varied tables of numbers.

A less immediately obvious, but undeniable application for a difference engine is all of the accountants and workers responsible for ensuring sufficient supplies. Given a certain number of expected miles of construction, how many railroad ties does one need to order? How much rail? When should you send the shipments of materials to optimize the number of trains you send, without losing valuable work time for lack of parts? Indeed, the benefit to accounting and management might have been greater than the advantages for the engineers.

Had the difference engine been available in 1863, would it have had any lasting impacts in the context of the railroad, or would it merely have eased the burden on overworked engineers and accountants? It’s hard to say. Even if use of a difference engine had made it cheaper to construct the railroad, it might not have been completed any sooner – the primary delays were caused by bad weather and treacherous conditions. Where the tables derived from a difference engine might have been more useful would have been for the hundreds of people starting new businesses in the recently opened up territories of the west. The railroad lead to a massive expansion of the population in the western US, and to be certain, many of them would have found the tables that a difference engine would have made available to be quite handy.