In 1919, as American factories were being reshaped by Taylorism, stopwatches, and the first generation of precision measuring instruments, John Lord Bacon and his co-editor Edward R. Markham published the third edition of a working textbook for blacksmiths and heat-treaters. In their preface, tucked between announcements of new gauges and modern methods, they left a warning that reads today like a shot fired directly at the automation debates of our own century.

The introduction of heat measuring and hardness testing instruments, together with various other modern appliances, and up to date systems of doing work have made necessary a broader knowledge of heat-treating methods than was formerly the case: for after all the most important factor is the man doing the work.

Notice the argument's shape. Bacon does not dismiss the new pyrometers and Rockwell testers arriving in shops around 1919 — he embraces them. But he inverts the expected conclusion. More instruments, he says, do not reduce the demand on human skill. They increase it. A worker who once judged steel by color alone now had to reconcile his eye against a thermocouple, understand what the instrument was measuring, and know when to trust it.

Was Bacon right? A century of research suggests he was well ahead of his time. Modern work on what Lisanne Bainbridge called the "ironies of automation" (1983) argues almost exactly this: automating a process does not eliminate the human operator but transforms their role into something harder — a supervisor of instruments who must intervene precisely when the automated system fails. Studies of aircraft cockpits, radiology reading rooms, and even self-driving cars keep rediscovering the point Bacon made in a chapter on hot iron.

The forge shop of 1919 offers an unusually clean case. Consider what "the man doing the work" actually needed to know:

• How the true color of hot steel differs under gaslight, sunlight, and the shadow of a shop wall — because a pyrometer only reads one spot.
• Whether a hardness tester's indentation was giving a valid reading on a decarburized surface, or lying about the metal beneath.
• When a piece was "soaking" evenly versus merely surface-hot — a judgment the instruments of 1919 could not make for him.

The dedication of the book — "TO ALL WHO WOULD ATTAIN, WITHOUT WHOSE ASSISTANCE IT WOULD NEVER HAVE BEEN WRITTEN" — is aimed squarely at working smiths, not managers. Bacon was defending a piece of practical wisdom that the coming century of scientific management would spend enormous energy trying to erase: that tacit craft knowledge is not a residue to be measured away, but the substrate on which measurement itself becomes useful.

When you next hear a claim that AI or automation will "eliminate" a skilled trade, it is worth remembering a Chicago forge instructor who watched the first pyrometers arrive in his shop and concluded, quietly, that they would make his craftsmen more important, not less.