Bench Degree·ELECTROMAGNETISMchapter

On the Cover

How the cover of every Bench Degree volume is chosen. One question, and it is not who got there first or who is famous. If we could bring anyone back to teach you this subject, who would you actually want at the bench? That is the whole test. It picks people who did the work with their hands, who checked things themselves, and who would be worth standing next to. Every one of them actually lived, which is why a cover portrait in this series is either a real document or openly a drawing, and never a photograph of something that did not happen.

Nikola Tesla, engraved from a studio portrait made in New York about 1890, when he was thirty-four.

He is not here for the coil, the war of currents or Colorado Springs. Those are Chapters 10, 9 and 13, and they are the parts of him everybody already owns.

He is here for Chapter 7, in which nothing moves.

The rotating magnetic field is two coils at right angles, fed by currents a quarter of a cycle apart, making a field of constant strength that points somewhere new at every instant. No brushes, no commutator, no sliding contact. He worked it out before he had a workshop to test it in. The induction motor in your refrigerator, your furnace blower and your well pump is that idea, unchanged in principle since 1888.

The second reason is harder. Chapters 13, 14 and 15 do little but separate what he did from what is claimed for him, item by item. Most famous names come out of an audit like that smaller. He comes out larger.

Michael Faraday is all over this volume and on none of its covers, and that is deliberate. He is promised one of his own later in the series.

About the portrait. The source is Napoleon Sarony’s studio portrait, made in New York around 1890 and published in the United States that decade, which puts it in the public domain there. A program converts it to line work, setting each line’s thickness from the local tone of the photograph. That is arithmetic on a real document. No generative model touched it, and no part of his face has been altered or completed.

The famous pictures of him reading in the Colorado Springs laboratory while discharges cross the room are multiple exposures, shot by Dickenson Alley in 1900. He is real and the discharges are real. They were never both there at once, and Chapter 13 hands you a camera so you can make one yourself.

The rule for this series is that a cover portrait is a document or it is openly a drawing, and it is never a photograph of something that did not happen.

The full account of how this book was made, including which parts were written with the help of a language model, is on the copyright page and on the back cover, itemised using the five credits published at bookcredits.org.

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