When Sir Arthur Conan Doyle decided to try his hand at writing detective stories, he was determined that chance would play little or no role in the solution of the crime. Sherlock Holmes would reason his way to the answer using both old and new forensic methods. In this way Holmes and Watson are presented as men of science. Even their conversation is on a lofty scientific level. When reading Sherlock Holmes, be prepared to hear about conic sections and surds and the 5th proposition of Euclid. Fear not however, much of the science is used just to set the mood of the story. But Holmes does solve a number of his cases using scientifically based forensic methods. He truly is the first scientific detective in fiction.
My new book, The Scientific Sherlock Holmes (Oxford University Press), examines the science and forensics that Holmes employed and even makes the case that it is the science that has made the Holmesian Canon so enduring. Here we'll examine his use of three techniques that were well established at the start of his career: footprints, decryption of ciphers, and handwriting analysis. Then we'll see how Holmes was at the forefront of innovation in solving crimes using fingerprints, dogs, and the idiosyncrasies of typewriters.
Holmes used footprints in the very first of the 60 stories, A Study in Scarlet, published in 1887. He was still using them in The Lion's Mane, which came out in 1926 as the 57th story in the series. In fact, there is footprint evidence in about half of the tales. Holmes's best use of footprints occurs in The Boscombe Valley Mystery, the sixth story, which he solved almost entirely on footprint evidence. After examining the ground around the site of the murder, Holmes tells Inspector Lestrade, "The murderer is a tall man, left-handed, limps with the right leg, wears thick soled shooting boots, and a gray cloak, smokes Indian cigars, uses a cigar holder, and carries a blunt pen-knife in his pocket." Despite Holmes's clue, Lestrade fails to apprehend Mr. Turner. Readers, however, are not surprised by the amount of detail in Holmes's description of the culprit. We have known since the second story, The Sign of the Four, that Holmes is an expert in footprints. There we learned that he had already penned a monograph entitled, "The Tracing of Footsteps with Some Remarks on the Uses of Plaster of Paris as a Preserver of Impresses". Indeed, throughout the Holmesian Canon our hero must deal with footprints on a wide variety of surfaces: clay soil, mud, snow, carpet, ashes, and blood.
Holmes wrote another monograph in which he analyzed 160 separate ciphers. Borrowing from Poe's The Gold Bug, Conan Doyle has Holmes use frequency analysis to solve the cryptic messages in The Dancing Men. Waiting until he has sufficient data, Holmes uses the fact that "e" is the most commonly used letter in English, and proceeds from there to the answer. In The Gloria Scott Case the cipher Holmes must solve is one that uses only every third word in the message. This same technique was used by union spies during the Civil War. Young followers of the 1940's radio show "Captain Midnight" were told to do the same thing with their decoder rings. In The Valley of Fear Holmes realizes that the cipher, just like one used by Benedict Arnold in the Revolutionary War and Abner Doubleday in the U.S. Civil War, employs a book. The message contains page and word numbers.
In Conan Doyle's time handwriting analysis was more trusted than it is today. Holmes was up to date and used handwriting to make some amazing deductions. Not only could he tell gender, but he was also able to make deductions about the writer's character. In The Reigate Squires he correctly proclaims that two writers are related. A clever deduction at the start of The Norwood Builder enables him to immediately discern the culprit. Holmes realizes that the shaky handwriting in Jonas Oldacre's will was due to its being written on a train. Knowing that no one would write such an important document in such a fashion, Holmes knows Oldacre is his man.
When we look at Holmes as a scientific innovator we find that he used some methods before actual law enforcement agencies did. For example, the use of fingerprints for identification was adopted by Scotland Yard in 1901. The first Holmes case to involve fingerprints was The Sign of the Four, published in 1890. We still read about fingerprints in The Three Gables (1926), though only in The Norwood Builder do fingerprints play a significant role. Still, Conan Doyle chose to have Holmes use fingerprints and not the rival technique of Bertillonage or anthropometry. Holmes the forensic scientist must have recognized the superiority of fingerprinting.
Holmes has also written a monograph on the use of dogs in detective work. Indeed, dogs play a significant role in several stories. Twice Holmes employs dogs to follow the movements of people. In The Sign of the Four, Toby fails to properly follow the odor of creosote to locate Tonga, the pygmy from the Andaman Islands. Instead Toby takes Holmes and Watson to a creosote factory. But in The Missing Three Quarter Pompey successfully follows the smell of aniseed and locates Godfrey Staunton. Holmes has another dog success in the 60th story, Shoscombe Old Place. Suspecting that Lady Beatrice Falder is missing Holmes uses her dog to demonstrate that her carriage is occupied by another woman. Early usage of dogs shows Holmes again at the forefront of detection.
There is one Holmes story, A Case of Identity (1891), in which the idiosyncrasies of a typewriter provide the evidence that leads to the solution. Holmes realizes that the key to the mystery is that Mary Sutherland's suitor only communicates by typewritten letters. Even his name is typed, there is no signature. Holmes manages to get a typed note from his suspect. The exact match of typed idiosyncrasies closes the case. In the United States the FBI did not start its document analysis section until over 40 years later, in 1933. We're told that the prolific Holmes is the author of a monograph entitled "The Typewriter and its Relation to Crime".
Sir Arthur Conan Doyle was a voracious reader. As a result he was well informed on a great many topics. His ability to weave a mixture of old and new crime detection techniques into the Sherlock Holmes stories is a big factor in their continuing appeal. The Scientific Sherlock Holmes demonstrates that science plays a big role in the continuing popularity of the greatest detective in fiction.