Philadelphia’s Forgotten Inventor: The Untold Story of Rudolph M. Hunter

Based on a c. 1925 photograph, this oil-on-canvas portrait of Rudolph M. Hunter was painted by Emilie DeSilver Atlee in 1976 and is now in the collection of the Franklin Institute.
Franklin Institute/Photo by David D. Hursh

The lot at 3710 Chestnut Street in Philadelphia is all but empty now – a low scraggly hedge in front, a scattering of shade trees, a long concrete walk on the right, skirting Penn Newman Catholic Center. It’s hard to imagine the fanciful Victorian mansion that once adorned the site – a “pretty residence of brick,” the Philadelphia Press unimaginatively put it in 1893, with “a pleasant portico and a conservatory at one side.” It was later dubbed “the Castle” by the owner’s grandchildren, for its battlements and soaring turret. But the most intriguing feature of the house lay behind the parapets, all but hidden from the street below. There, running the length of the long, flat roof was a working trolley line.

The Castle’s owner was Rudolph Melville Hunter, holder of more than 140 patents for electric railway devices and systems. So the rooftop trolley wasn’t there just for his or the family’s enjoyment. He had built it to test new designs and “fulfill the requirements of the patent law.”

Hunter was born on June 20, 1856, in New York City. He attended schools in England, France and Canada and then gained practical experience working as a draftsman and engineer in Cincinnati and Ironton, Ohio, and elsewhere in the Midwest. He resumed his formal education in 1876 at Philadelphia’s Polytechnic College of the State of Pennsylvania, where he studied mechanical engineering. Once in Philadelphia, he stayed. He earned his degree in 1878, married in 1879, and established the Patent Offices of Rudolph M. Hunter by 1880, offering his services as a consulting engineer and patent attorney.

But he was first and foremost an inventor. His first patent (No. 216,519), for a “process and apparatus for manufacturing illuminating gas,” was issued in June 1879. He would eventually hold 299 U.S. patents, all but 20 of them issued by 1902. He attributed his incredible productivity to his ability to spend long hours, with little sleep, in his office or lab. “I always work from twelve to fifteen hours a day,” he told the Press, “and many a day I have worked eighteen hours.”

His inventions ranged from toy banks and printing machines to a submarine. Befitting the times, most were electrical. He was not only a witness but a significant contributor to one of the world’s great technological achievements – the harnessing of electricity as a useful source of power.

Not every house in West Philadelphia had a rooftop trolley, it’s safe to say, but Hunter’s “Castle” at 3710 Chestnut Street did. From “A Trolley Road on a House,” Philadelphia Times, January 2, 1898

Electric Railways

By 1887 Hunter had formed Hunter Electric Co., soon reorganized as Electric Car Company of America, to “manufacture and introduce” his electric railway inventions. Electric Car’s executive team included two very well-connected Philadelphians, William Wharton Jr. and Wharton Barker. Both were also affiliated with Wharton Railroad Switch Co., and by January 1888 Electric Car had taken over that company’s “extensive” works on Washington Avenue.

On this sketch and description of an electric locomotive, signed by Hunter and dated October 15, 1879, the side-mounted underrunning trolley appears to lack a provision for lateral movement, a feature that would prove essential.
Courtesy Margaret DeSilver Hursh

But just as Electric Car was settling into its new works, an event that would dramatically affect the company’s prospects was unfolding in Richmond, Virginia. There, an inventor named Frank Sprague (1857-1934), facing a host of technical problems and an impossible deadline, was working frantically to complete the city’s new street railway system. The Richmond line – the world’s first successful large-scale electric street railway system – opened for regular business in February, and by that fall it was operating reliably and economically.

Sprague’s success sparked an electric railway boom. It also, not surprisingly, spurred the efforts of the country’s largest and most powerful electrical companies to build their own electric railway businesses, mainly by acquiring the patents and expertise of outside inventors. Sprague had been financed by associates of Thomas Edison, and in April 1889 his company was folded into the newly formed Edison General Electric Co. Edison General’s most formidable rival, Thomson-Houston Electric Co., had already bought out Sprague’s leading rival, Charles Van Depoele (1846-92), and hired him as a staff engineer. The company then set its sights on other inventors, including Hunter.

This early design from an 1884 Hunter datebook appears to have all the underrunning trolley’s essential features.
Courtesy Margaret DeSilver Hursh

In August 1889, according to the Boston Daily Advertiser, Thomson-Houston bought Electric Car’s “right, title and interest to electric car propulsion by either overhead or underground wires.” The deal included the rights to “many valuable patents and inventions of Rudolph M. Hunter, [George H.] Condict, and others,” but only, Hunter would later note, as those patents applied to vehicles powered by external (“overhead or underground”) conductor wires. Electric Car retained its rights to the patents, as they applied to battery-powered vehicles.

The competition between Edison General and Thomson-Houston was fierce and costly, all the more so as they battled for control of the electric railway industry. By early 1892 the rivalry had grown too costly to bear, and the companies suddenly agreed to end it by merging. One of the deal’s key benefits would be to bring both partners’ many patents – including the Electric Car patents controlled by Thomson-Houston – together in a single organization. The merger was consummated in April, and one of the Electric Car patents (not a Hunter patent but one to which he was intimately tied) would quickly prove valuable to the new corporate giant, General Electric Co.

Recognition  Proves  Elusive

Studio photograph of Hunter, 1890s. Courtesy Elizabeth Atlee Carapico

In 1894 Hunter entered the Franklin Institute’s annual competition to honor significant inventions and scientific discoveries. His goal was to “secure the proper recognition” for his electric railway work, and in a letter to the institute’s secretary, William H. Wahl, he claimed nothing less than to have invented the “modern electric railway . . . from the central station to almost the smallest electrical details of the entire system and rolling stock.”

It was a bold claim to say the least. The electric railway’s roots date back to at least 1835, when a self-taught engineer named Thomas Davenport (1802-51) built a rudimentary electric railway model. Edison experimented with electric locomotives starting in 1880, and in 1881 the German firm Siemens & Halske installed an electric streetcar line near Berlin. By 1883 several inventors, most notably Van Depoele, had demonstrated electric locomotives or streetcars in the U.S., and in 1886 as many as 13 electric railways were in operation worldwide. Those developments, and many others, had set the stage for Sprague’s success in Richmond.

In his official entry, submitted to the Franklin Institute’s Committee on Science and the Arts, Hunter was at least somewhat more realistic. He claimed credit less for the electric street railway as a whole than for two of its key components: the “trolley system” (specifically, a practical underrunning trolley, in which the contact device runs along the underside of an overhead conductor wire) and the “series-multiple controller” (a switch used to control the speed and power of cars). He submitted 11 patents – nine for the trolley and two for the controller – in support of his claims.

The committee, despite Hunter’s patents, denied him an award. “Other inventors,” a report on his entry noted, “are popularly credited with the invention of one or more of the essential parts of the trolley system.” That argument held no sway with Hunter, who claimed that he had been first to conceive a viable underrunning trolley and that others had been given unfair credit for it. But the report also noted that the committee was ill-equipped to conduct an investigation to determine priority of invention, a task that properly belonged to “the courts.” Hunter was outraged. “This committee,” he railed in a second letter to Wahl, “has done its best to injure the man who has worked harder and done more than any other to develop the art of this great industry.”

But his outrage was far from justified. The U.S. Patent Office, in a landmark interference case, had in fact already determined priority of invention. The case had pitted Hunter against both Sprague and Van Depoele. It opened in January 1889 and ran four long years until February 1893, when the examiners-in-chief named Van Depoele the underrunning trolley’s rightful inventor. He had died almost a year earlier, however, and his patent (No. 495,443) was assigned to Thomson-Houston (by then part of General Electric). It turned out to be one of the electrical industry’s most valuable and hotly contested patents – the subject of at least eight infringement suits brought by Thomson-Houston. In case after case, the courts affirmed the patent’s validity, in the process giving GE a virtual monopoly on the underrunning trolley. The patent was eventually ruled invalid, but only because it had been anticipated by an earlier Van Depoele patent.

This appears to be an Electric Car Company of America prototype or mockup. The photo was probably taken at the company’s works, which covered a full block at 23rd and Washington in Philadelphia.
Courtesy Margaret DeSilver Hursh

Hunter’s claim to have invented the series-multiple controller, more commonly called the “series-parallel controller,” lay on slightly firmer ground. He based it mainly on a patent (No. 385,055) issued to him in June 1888. Some six years earlier, English electrical engineer John Hopkinson (1849-98) had been granted a British patent for virtually the same invention. In 1892 Hopkinson applied for a U.S. patent, triggering an interference case against Hunter. Hunter produced evidence that he had conceived his invention by January 1881, a year before Hopkinson’s “date of invention” (which for purposes of the case was ruled to be January 7, 1882, though he had actually conceived his invention at least six months earlier). But despite Hunter’s evidence, the examiner of interferences granted priority of invention to Hopkinson. Hunter, the examiner explained, had “established conception in 1881” but failed to show “reasonable diligence” in attempting to reduce his invention to practice before Hopkinson’s date of invention.

Hunter appealed to the examiners-in-chief, then to the commissioner of patents. The commissioner declined to rule on the decision awarding priority to Hopkinson, but he noted that Hopkinson’s British patent had expired, which made him ineligible to receive a U.S. patent (his U.S. patent, had one been issued, would have expired on the same date as his British patent). That left Hunter’s claim to be the series-parallel controller’s inventor at least somewhat open to debate. The Patent Office had denied him priority of invention, but still he could claim prior conception (though possibly only on a technicality, the assignment of an arbitrary “date of invention” to Hopkinson). His patent, moreover, remained in force.

Hunter apparently failed to realize, when he entered the 1894 competition, the full extent of his contribution to electric-railway motor control. Before the advent of series-parallel control, rheostatic control – the use of rheostats to increase or decrease the resistance in motor circuits – was the standard control method. In November 1888, five months after Hunter’s series-parallel control patent was issued, George H. Condict (1862-1934) patented a controller that improved on Hunter’s design, in part by combining series-parallel and rheostatic control in a single switch. Condict developed his controller, according to Hunter, “in connection with my work,” and that clearly was the case – Condict was Electric Car’s general manager and Hunter served as his patent attorney.

These trolley sketches marked “Hunter Exhibit Drawing No. 11” were apparently entered as evidence in Hunter’s interference battle with Frank Sprague and Charles Van Depoele. The case was plagued by delays, in part due to the demands of at least 10 other interference cases in which Hunter was involved. Courtesy Elizabeth Atlee Carapico

Condict’s patent (No. 393,323) turned out to be the most important of the Electric Car patents licensed to Thomson-Houston. In 1892 Thomson-Houston engineers (by then working for GE) developed a controller “constructed under the Condict patent, with modifications.” The new controller was so successful that it became the industry standard in the U.S. It was also closely imitated by rival companies, and Electric Car and Thomson-Houston responded with at least four suits for infringement of Condict’s patent. Those suits were successful at first, but in 1901 a U.S. circuit court partially invalidated the patent. “Mixed control,” the court ruled, had been anticipated by another inventor – none other than Hunter. The court cited two Hunter patents (Nos. 385,180 and 431,720), both of which describe the combined use of series-parallel and rheostatic control. Neither patent specifies, however, the use of a single switch to implement both control types. The court therefore credited Hunter with the invention of mixed control as a broad method, while upholding Condict’s patent with regard to the use of a single switch to implement that method.

In 1896 Hunter entered the Franklin Institute competition again on an assertion no less audacious than his claim to have invented the electric street railway. He had invented, he wrote in his official entry, the “‘step up and step down’ transformer system of electrical distribution.” Step-up and step-down transmission and distribution, still in use today, is the method by which electric current is stepped up to high voltages for long-distance transmission and stepped back down to safer, useful voltages at local distribution points.

In support of his claim, Hunter submitted a patent (No. 460,071) issued in 1891 and assigned to Thomson-Houston. He also submitted drawings showing that he had conceived a step-up and step-down system in 1881 and reduced such a system to practice in 1884.

Again, the Committee on Science and the Arts denied him an award. A report on his entry noted that other inventors, starting with Joseph Henry in 1838, had demonstrated the use of a transformer to step up a current to a higher voltage and a second transformer to step it back down. Hunter, therefore, hadn’t been first to conceive step-up and step-down transmission as a broad method. But that left the question of whether he had been first to point out the method’s “economy,” or practical utility. In March 1881, the report noted, Marcel Deprez and Jules Carpentier had applied for a French patent for a step-up and step-down system capable of powering an electrical device at a remote location. Hunter claimed to have conceived his system by August, some five months after Deprez and Carpentier’s application; therefore he hadn’t been first to recognize the method’s utility.

Electric Automobiles

In the late 1890s the outlook for electric automobiles seemed bright, and a host of inventors and vehicle makers took aim on the market. Hunter, not surprisingly, was among them. In 1898 he joined three prominent Philadelphia businessmen – William D. Marks, John A. Brill and John H. Noblit – to form General Electric Automobile Co. The company touted its control of some 70 patents, more than 40 of them Hunter’s, that it claimed to cover “practically all of the devices and appliances of value” in the construction of battery-powered vehicles. They were mostly, if not all, Electric Car patents, the rights to which had been transferred to GE Auto.

GE Auto made both passenger and commercial vehicles, and at least two passenger models were sold by John Wanamaker & Co. Wanamaker’s full-page ad in The New York Times of April 7, 1900, offered the Runabout for $1,200 and the more “sumptuous” Brougham for $3,000.

The ad gave no hint, however, that GE Auto was in serious financial trouble. In March a committee had been formed to seek “the consolidation of this company with other automobile companies” or to provide “adequate working capital.” By June the company’s stock price had collapsed, and the Times reported that a new corporation would be formed to take over its property. It’s unclear, however, exactly how GE Auto met its demise. In July rights to the company’s patents were sold at public auction to James W. Cunningham of New York City. The $29,000 sale price, the Philadelphia Times noted, covered “less than half the company’s indebtedness.” GE Auto’s stock apparently continued to trade at less than a dollar a share until at least May 1902, but there’s little evidence that the company conducted any meaningful business after the sale of its patent rights.

Motor Trucks

Hunter’s quest to develop and commercialize electric vehicles – first the street railway, then the automobile – had come to an unceremonious end. But he hadn’t quite exhausted his interest in motor vehicles. In 1901 he was granted a patent (No. 670,405), and in 1902 a second patent (No. 696,143), for vehicles powered by “gasolene” engines (or other motor types). He assigned both patents to yet another of his companies, Tractor Truck & General Power Co.

Hunter’s 1902 motor truck patent. It doesn’t take too much imagination to see the modern semitruck in this innovative design. U.S. Patent and Trademark Office

The 1902 patent, according to a 1920 automotive reference guide, was the first for “short wheel-base motor trucks used with two-wheeled or semi-trailers.” Hunter’s design combined all the basic elements of the modern semitractor – the motor, drive wheels, steering wheels, vehicle controls and a fifth-wheel trailer hitch – in a self-contained unit. His key innovation was to place the driver’s seat not on the trailer, as in previously patented designs, but on the tractor. He had envisioned the tractor as an independent vehicle, not simply as a source of motive power – a replacement for the horse.

It’s unlikely, however, that he was first to conceive the semitractor. That honor may belong to pioneering automaker Alexander Winton (1860-1932). In about 1899 his Cleveland-based Winton Motor Carriage Co. made a tractor-trailer combination designed to transport automobiles. But Winton didn’t patent a semitractor design, and Hunter’s patent does appear to be the first, in the U.S. or elsewhere, for a self-contained motor truck specifically designed to haul a semitrailer.

Little information on Tractor Truck is available. The company apparently never produced or commercially operated vehicles, and in 1913 rights to the two Hunter patents were sold to Charles H. Martin. Martin later formed the Martin Rocking Fifth Wheel Co., which successfully produced hitches based in part on the “rocking” fifth-wheel design included in Hunter’s 1902 patent.

Unlikely Alchemist

By 1903 Hunter had achieved more than most inventors ever would. His 279 U.S. patents ranked him among the most prolific patentees of his era, and his financial reward had been far from paltry – “more than six hundred thousand dollars,” he hinted in 1894, for the rights to his electric railway patents. But he had endured, in return, “the most incessant labor that a man ever had,” and despite the grueling work and years of legal wrangling, he had failed to gain the recognition he thought he deserved. Maybe it’s not surprising, against that backdrop, that his career would take a major turn. But who could have imagined how dramatic that turn would be?

In a string of newspaper articles, the first published in July, he claimed to have discovered a process by which he could transmute silver and other metals to gold – he had achieved, in other words, the alchemist’s dream. He planned to capitalize on his discovery by building a $500,000 plant in Philadelphia to “manufacture” gold, and he formed two companies – Mirabile Corp. and United States Assay and Bullion Co. – to carry out the plan.

Hunter’s claim, as far-fetched as it seems today, wasn’t completely out of step with mainstream science. Thorium radioactivity, physicist Ernest Rutherford and chemist Frederick Soddy had reported in September 1902, is “accompanied by chemical changes in which new types of matter are being continuously produced,” and “these chemical changes must be sub-atomic in character.” Their research had confirmed, in other words, that transmutation occurs in nature. Less than a year later, just as Hunter was making his transmutation claim public, chemist William Ramsay (1852-1916), also working with Soddy, reported that radium, in the process of radioactive decay, transmutes into helium. Hunter, hearing that news, wrote to Ramsay and informed him that he had already changed silver into gold. Ramsay was intrigued enough to write Hunter “several times” and visit him in Philadelphia in September 1904. “The gold man,” Ramsay wrote in a subsequent letter to his wife, is “all right – no swindler.” And in a 1906 letter to a close friend, he noted that Hunter had “based his conclusions on actual experiments, and he gave a reasonable theory.”

Hunter takes his family for a ride on a powerboat during a vacation in the Thousand Islands, near Alexandria Bay, New York, c. 1906.
Courtesy Elizabeth Atlee Carapico

Ramsay’s interest was bound to wane, however. Hunter sent him samples of his processed silver, in which gold was supposedly “growing.” Ramsay observed them for years but found that their gold content, which may simply have resulted from impurities, didn’t change. He found no evidence, in other words, that Hunter’s process had worked.

Rutherford achieved the first scientifically documented artificial transmutation – the conversion of nitrogen into an oxygen isotope – in 1919. And it is possible, we now know, to change other metals into gold; it can be done in nuclear reactors and particle accelerators. But “manufacturing” gold in commercial quantities from silver, or any other element, remains a practical impossibility.

Hunter insisted, nonetheless, that his transmutation process worked and his gold-manufacturing plans would soon be realized. He even claimed by 1916 to have “mastered” transmutation to the point where he could produce gold from “common mineral substances, even from water and stone.” But the $500,000 plant was never built, and Mirabile, according to the Galveston Tribune, fell into disarray. The company apparently built a “laboratory” on Spruce Street, but “difficulties in operation caused the inventor’s plans to temporarily fail.” Hunter subsequently bought more than $33,000 in stock from disgruntled investors, and in 1916 his elder son, Rudolph Harding Hunter, tried to seize control of the firm.

There’s no concrete evidence, on the other hand, that Mirabile intentionally deceived or defrauded investors. So it remains possible, if not likely, that Hunter truly believed his claims. How that could be remains a mystery. He clearly should have been able to determine, as Ramsay did, that his transmutation process didn’t work.

Even as he chased his transmutation dreams, Hunter never completely abandoned his career as a mainstream engineer and inventor. He was granted 20 U.S. patents after 1903, at least nine of them for hydraulic devices, such as nozzles and valves. His last patent (No. 1,925,096), issued in September 1933, was a mold for making reflective prism-glass.

Hunter died March 19, 1935, having never publically disavowed his transmutation claims. His remains lie with those of his wife Emilie and younger son Robert in the deteriorating art deco mausoleum at Chelton Hills Cemetery in North Philadelphia.

The New York Times, in eulogizing Hunter, did little more than parrot highly suspect information from Who’s Who in America. The obituary plays up his claim to have “discovered and commercialized transmutation of the elements,” while all but ignoring his most significant legitimate accomplishments; there’s barely a mention of his electric railway work and not a word on his pioneering semitractor patent. The transmutation claim had surely originated with Hunter, so the Times in repeating it had only done him cruel justice. He reaped what he had sewn, and many a reader was content, no doubt, to write him off as a crackpot, or worse.

But the would-be alchemist was also an accomplished engineer and inventor – a legitimate contributor to some of the most advanced technologies of his day. His contributions were modest, perhaps, in comparison to those of his more illustrious peers, but no less deserving of recognition. His development of mixed control, for example, may pale before Sprague’s achievement at Richmond, but it was a significant advance, one for which both he and Condict clearly deserve credit.

Hunter’s faults and missteps can’t be easily dismissed. But he was, despite them, a highly skilled and remarkably prolific inventor, and it would only be fair to resurrect him from the ranks of the forgotten.

David D. Hursh lives in Lewisburg, Union County, and has written for the Gorilla Foundation’s journal Gorilla and a variety of crafts magazines. He admits to having more than a scholarly interest in Rudolph M. Hunter, his great-grandfather.