WE CAN THANK the world’s first consulting detective for conceiving manual forensics, identifying criminals (and the rest of us) by examining the person’s hands. In The Sign of Four, one of four novel-length chronicles, Holmes refers to his “curious little work upon the influence of a trade upon the form of the hand, with lithotypes of the hands of slaters, sailors, cork-cutters, compositors, weavers, and diamond-polishers.”

Holmes at work. Image by H.B. Eddy, from The Sign of the Four, San Francisco Call, October 1907. The title’s second “the” was used in an early printing of the tale.
While this only slightly winnows the field of all possiible culprits, it does encourage us to think about what to expect of the hands of these workmen. But who are they? Sailors, weavers and diamond-polishers are still employed. But what of slaters, cork-cutters and compositors?

“Our guide knocked with a peculiar postmanlike rat, tat.” From The Sign of the Four.” Do you suppose Holmes studied knuckle raps as well?
Even the familiar occupations generate Sherlockian controversy, as detailed in The New Annotated Sherlock Holmes, three volumes, edited with notes by Leslie S. Klinger, W.W. Norton, 2006. Despite what Holmes says, a footnote in Volume 3’s The Sign of Four questions a sailor’s hand: “Nothing specific would distinguish a sailor’s hands from those of another person working hard outdoors … ships chores are more varied than repetitive, and furthermore … the right and left hands are used equally.”
Maybe this is akin to Holmes’ observation in ”Silver Blaze” about the remarkable dog that didn’t bark in the night. How curious: The man’s right and left hands didn’t look different.
Similarly for a weaver’s hands. The footnote observes that, granted, there are specific workers with industrial looms: “the doffer, the quiller, the hooker, the mule spinner, etc.” However, what of a less-than-industrial-strength hand loomer?
Holmes provides a clue about this in “The Adventure of the Copper Beeches” when he says, “Pshaw, my dear fellow. What do the public, the great unobservant public, who could hardly tell a weaver by his tooth or a compositor by his left thumb, care about the finer shades of analysis and deduction!”
Hmm. A weaver’s tooth? I asked Wife Dottie, whose weaving has already been discussed here at SimanaitisSays. She said she hadn’t heard of it. I queried the Internet and found perhaps it’s a snaggle tooth from repeated biting or cutting a yarn when the hands are busy with other weaving tasks.
The compositor’s left thumb is easier to define, though I suspect Print Shop is no longer part of the middle school curriculum these days. A compositor used to set movable type. (What’s “type,” Grandpa?)
Setting type is a tedious process, complicated by the fact that all those tiny pieces of type have their letters reversed and upside down. One by one, each letter is assembled into a line of type contained in a gizmo called a composing stick. The compositor held this object in the left hand, and used the left thumb to secure the pieces of type as they were added.

A compositor at work: The left hand holds the composing stick; the thumb secures the pieces of movable type prior to their being fixed in place. Image from Tennessee Newspaper Digitation Process.
Do this as a profession, and your left thumb will develop a callus, not to say a permanent ink stain. Pieces of type were used over and over.
So, one mystery solved. But what of cork-cutters and slaters?
According to the footnote, manual cork-cutting would lead to calluses “produced on the thumb and first two fingers of the left hand by grasping the cork, and similarly on the thumb and across the inside of all four fingers of the right by the handle of the knife.”
Last, a slater was a builder of roofs at a time when slates were the chosen material. A footnote suggests looking for “fingertips of the left hand worn smooth by handling the stone, as seen also in masons and bricklayers … and calluses across the right palm from gripping the hammer.”
How to tell a slater from a mason or bricklayer? “It is also reasonable that callosites of the knees would be prominent … since roofing is done chiefly in a kneeling position.”
Pshaw, my dear fellow, got it! ds
© Dennis Simanaitis, SimanaitisSays.com, 2016