Roget seems to have been interested in and learned about almost everything. I first came across him when I was investigating the circumstances of the 1831 awarding of a medal by the Geological Society of London. A geologist named William Smith, who had for many years been ill-used by his peers, was, after a scandalous delay, being formally recognized. I wanted to know who those peers were, and who had so wisely engineered Smith's reappraisal. I needed a list of those who attended the award ceremony.
The Geological Society had the relevant papers in its archives, and the dusty volume holding them was duly brought to me. It was opened carefully by a librarian, who found the proceedings of the meeting and scanned the handwritten list of those present. It was much as I had expected: the meeting had been chaired by the renowned Adam Sedgwick, and the attendees included William Broderip, the Reverend William Whewell, Leonard Horner, Captain James Vetch, the Henry De la Beche who would go on to be the first head of the British Geological Survey, Professor Edward Turner, the great Silurian expert Roderick Murchison, and one Dr. P. M. Roget. The librarian gulped. "Bless my soul," she said. "Do you think it could be him?" We looked in the index of members and found that Peter Mark Roget had indeed been a fellow of the Geological Society—and of many, many other august bodies besides.
The title page of the first edition of his Thesaurus offers tantalizing clues to his brilliance: his geological inclinations are shown only in the string of initials after his name ("M.D., F.R.S., F.R.A.S., F.G.S."), but he is also identified as "Fellow of the Royal College of Physicians; Member of the Senate of the University of London; of the Literary and Philosophical Societies etc. of Manchester, Liverpool, Bristol, Quebec, New York, Haarlem, Turin and Stockholm. Author of the 'Bridgewater Treatise on Animal and Vegetable Physiology,' etc."
The "etc." shrouds an array of other achievements. Even the sparse Britannica entry mentions that Roget invented the so-called log-log slide rule, that he was the secretary of London's fabled Royal Society, and that he was a philologist. A cursory look at his scores of published papers attests to his many other interests (and the fact that he wrote some of these papers in French, German, and Latin as well as English shows his formidable linguistic abilities, stemming from his Swiss Huguenot roots).
Roget's first published works were purely medical, though wide-ranging by any standards: a study of the effects of inhaling laughing gas, a test for detecting the presence of arsenic, how the skin changes color if a patient ingests silver nitrate, on sweating, on tetanus, on voluntary action of the iris, on perception and feeling in animals, on epilepsy, on the medical care of prisoners. By midlife he was starting to branch out to other topics. In 1815, when the rest of Europe was preoccupied with Waterloo, he published a paper titled "A New Instrument for Performing Mechanically the Involution and Evolution of Numbers"—that is, the slide rule. Three years later he produced papers on the kaleidoscope and Dante. He was fascinated by chess problems, too, and one of his more amusing papers shows that it is possible (if not necessarily desirable) to move a knight across every square of the board.
Then, in 1825, came his paper "Explanation of an Optical Deception in the Appearance of the Spokes of a Wheel Seen Through Vertical Apertures," which is regarded as seminal by modern historians of the cinema. The impetus for the paper came about by chance. Early one morning soon after his marriage, at home in Bloomsbury, Roget, according to Emblen, had been gazing up idly from his basement kitchen, from behind a vertical venetian blind, at the passing traffic. The slats of the blind, he suddenly noticed, broke the movements of passing carriage wheels into a jerky series of still pictures. Depending on the speed of the carriage and the position of his eyes, the spokes of the wheel appeared to bend, to curve sometimes backward, sometimes forward. When he moved his head up and down, he noticed that the image changed. He dashed outside and paid a driver a shilling to drive his carriage back and forth along the street while Roget jotted down notes and made sketches. All the while his new wife, Mary, was upstairs tapping her feet, waiting with the breakfast kedgeree cooling in the dining room. Life as Mrs. Peter Mark Roget was, she soon came to understand, invariably odd.
The paper her husband then published led in time to what Marshall McLuhan and others recognized, in Emblen's words, as "another dimension for human existence"—the motion-picture industry. For, as Roget concluded, "an impression made by a pencil of rays on the retina, if sufficiently vivid, will remain for a certain time after the cause has ceased." Persistence of vision had been discovered; the Zoetrope, the Praxinoscope, and the CinemaScope were just waiting to be invented, and 6,000 miles westward Hollywood awaited its founding.
But there was another, more soberly philosophical side to Roget's raft of achievements and ambitions. He seems to have been—sentimental though this may sound in today's cynical climate—a thoroughly good person, suffused with ideals about the society of which he was a privileged member. He held a profound belief in the right of ordinary men and women to know things—to be able fully to appreciate the wonders and complexities of the world. He was influenced by Jeremy Bentham's ideas of utilitarianism, which sought to promote the spread of happiness to the greatest possible number of people. He offered his medical services free to those who couldn't pay. He was a keen supporter of preventive medicine—urging reforms, for example, in London's water supply (and proposing a method of water filtration through sand that is still in use today). He was a founding member of the short-lived Society for the Diffusion of Useful Knowledge, and he wrote a series of sixpenny treatises—on electricity, galvanism, magnetism, and electromagnetism—that were intended to help poorer and less educated people learn what he and his kind already had the privilege of knowing.
He also (as already mentioned) contributed about 300,000 words to the well-regarded seventh edition of the Encyclopaedia Britannica. Of these, 150,000 words went for one major treatise, Physiology; the remainder were divided appropriately among the articles Ant, Apiary, Baldinger, Sir Joseph Banks, Barthez, Beddoes, Bee, Bichat, Brocklesby, Broussonet, Camper, Crawford, Currie, Deaf & Dumb, Kaleidoscope, and Phrenology (of which he was deeply scornful). Although some of these articles have survived, much cut, into the modern era (an article on Marie-François-Xavier Bichat, the French founder of the science of histology, is still there, and twice as long as the article on the man who first authored it), Roget's name does not survive in the index of the Britannica's contributors; today "PMR" is a blameless French museum curator named Pierre Rosenberg.
It remains one of the more curious aspects of Roget's life that in this fury of intellectual and socially reforming energy his deep interest in the English language did not become fully apparent until he was in late middle age. He was nearly seventy when, still living in his London townhouse, he began work on his Thesaurus, having just been forced from his post at the Royal Society to make way for younger, cleverer, more energetic scientists.