Frank J. Sprague, the man behind the motors that remade the urban landscape

Navigating the burgeoning cities of the early twentieth century would have been a very different experience without the electromechanical railway and elevator systems designed by Frank Sprague.

The basic layout of a modern metropolis – a core of skyscrapers surrounded by many square miles of densely packed business and residential districts – is something that we tend to take for granted. However, this arrangement presupposes technology that efficiently and reliably moves human bodies throughout three-dimensional urban spaces. In an era when cities were expanding in the x–y plane and buildings were lengthening along the z axis, an ambitious and brilliant engineer by the name of Frank J. Sprague developed the horizontal and vertical transportation solutions that modern society needed.

Frank J. Sprague, when he was president of the American Institute of Electrical Engineers.
Figure 1. Frank J. Sprague, when he was president of the
American Institute of Electrical Engineers.

The dynamo electric machine

Though he’s considered an electrical engineer, Sprague’s work leaned heavily toward the electromechanical side of the EE spectrum. His long and highly productive career as an entrepreneur, inventor, and innovator is somewhat difficult to encapsulate, but the throughline in his story is undoubtedly the electric motor.

Born in 1857, Sprague attended Drury High School in Massachusetts and demonstrated an aptitude for mathematics. He then studied at the United States Naval Academy in Annapolis, graduated in 1878, and entered service as an ensign in the Navy; his naval duties provided opportunities to experiment with electrical equipment and attend technology exhibitions in Europe. In 1881, while assigned to the USS Richmond, Sprague invented an inverted dynamo that he called a “dynamo electric machine,” and from then on his life was an assiduous pursuit of electromechanical innovation.

A drawing of an electric motor, from Sprague's own notebook.
Figure 2. A drawing of an electric motor, from Sprague’s own notebook.

After leaving the Navy, Sprague learned more about electric motors as an employee in the Edison Company. His active, disciplined mind was accumulating ideas for inventions, and in keeping with the ambitious, entrepreneurial spirit of the late nineteenth century, he quit his corporate job and started his own business. The Sprague Electric Railway and Motor Company sold numerous small motors for various types of industrial and residential machinery, but its most notable achievement was the pioneering electric railway technology that converted Sprague’s engineering startup into an international success story.

Horses out, motors in

In the mid-nineteenth century, urban mass transit was powered by horses. The transition from quadrupeds to electric motors was smoother than you might think, though, because many cities had already installed rails into the roadways in an attempt to make horse-powered transportation more efficient. Thus, the rails were already there, waiting for the technological innovations that allowed Sprague to surpass his predecessors and offer a truly feasible electric railway system.

Sprague’s innovative designs extended into the realms of control systems, suspension, braking, and power transmission. Among his various improvements to electromechanical devices and railway equipment, perhaps the most significant was a self-governing electric motor, i.e., a motor that could maintain constant rotational speed despite load variations. (I’m not a motor expert or a trolley expert, but considering the continual coming and going of passengers, I can imagine that without this functionality, the ride would be a rather lurchy one.) Also, if you thought (like I did) that regenerative braking is a relatively new technology, Sprague actually invented that in the 1880s – in his case, though, the vehicles were humble trolleys, not flashy Teslas, and no batteries were involved.

An 1880s electric trolley car, riding on rails and powered by overhead lines.
Figure 3. An 1880s electric trolley car, riding on rails and powered by overhead lines.

In addition to the improvements achieved by Frank Sprague the engineer, Frank Sprague the businessman published some observations in favor of his system. He noted that electric power would eliminate the sanitary problems and real-estate depreciation associated with an ever-increasing population of trolley-towing horses, arguing that with electric power, “the health and comfort of the whole population is conserved.” There’s a trivial but amusing touch of irony here – after a motor failure occurred during development of the first electric streetcar system in Richmond, Virginia, Sprague needed a team of mules to drag the disabled unit back to the shop.

Sprague faced serious technical challenges when building the first electricity-powered urban transit system, but one by one they yielded to his persistence and expertise. The Richmond electric trolley service went into operation in 1888, and from there Sprague’s technology spread rapidly across the United States and even into Europe. An article by historian Michael Robbins provides some impressive details:

By 1 July 1890 there were 914 miles [of street railway] electrified in the United States – twice as many as were steam-operated and more than three times the length of cable lines. Within three years 200 streetcar systems had been or were in the process of being converted, 50 per cent by Sprague’s company, more than 90 per cent based on his patents. Sixty per cent of all mileage was electrified by the end of 1893, 98 per cent ten years later.

He concludes that the “demonstration at Richmond proved to be a turning point such as can rarely be identified in the history of technology.”

The heroic inventor

In 1890, Sprague sold his Electric Railway and Motor Company and explored transportation opportunities in the vertical dimension. He applied his extensive experience with electric propulsion to the task of developing electrically powered replacements for steam and hydraulic elevators, and after a few years the Sprague Electric Elevator Company had delivered hundreds of units.

Sprague sold his elevator business in 1895 and returned to horizontal transportation, working on electrical systems for underground and railroad transit. During World War I he served as a technical advisor for the Navy, and he died in 1934 after a long life of innovation and ambitious entrepreneurialism.

Invention was a way of life for Frank Sprague – a fundamental aspect of his personal identity. According to historian Mark Gallimore, later in life Sprague viewed his engineering endeavors as “legendary technology adventures,” and he wanted to be remembered as a “heroic inventor.”

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