éBack to the Table of Contents

Question to Marilyn: "Why does the north end of a compass needle always point north? If like poles repel (and unlike poles attract), shouldn't the north end point south instead?"

Marilyn's answer: "The north pole of a compass needle does point south. It's the "north-seeking" pole that points to the Earth's magnetic north. So the end of the compass needle marked N (for north) is actually the south pole of compass needle. This is supposed to avoid confusion!"

Physicist's comments: It is Marilyn's answer that creates confusion!

Obviously, the end of a compass needle pointing to the Earth's geographic north is marked N. This end of the compass needle is also defined as the north magnetic pole, so everything is consistent so far. Consequently, it is the Earth's south magnetic pole that is located near the Earth's north geographic pole, while the Earth's north magnetic pole is located near the Earth's south geographic pole.

éBack to the Table of Contents

What caught my eye was the following sentence in the story “American, Abroad”:

"...Caroline Carmichael felt sheerly diamagnetic impulses..."

Physicist's comments: The author intended to indicate a strong attraction-repulsion dichotomy experienced by Caroline.

The word “diamagnetic” has a very precise meaning in physics: it is used to describe materials in which a reaction to applied external influence (magnetic field) tends to counter-act the external influence to the point of making it almost nonexistent.  A diamagnetic is a material inside which any externally applied magnetic filed will be greatly reduced.

Now, it may very well be that us, physics types, use the “di” prefix incorrectly. But for me, the meaning of the above quoted sentence is just the opposite of what the author intended to say.

So what word would a physics types use to express such  attraction-repulsion dichotomy?  They would say “magnetic dipole” to describe an object that has two poles (ends) of exactly opposite properties. Also, they would probably use a word “bipolar” to signal its attraction-repulsion characteristics.  Hence, as a physicist I'd prefer a different wording in the sentence, perhaps:

"...Caroline Carmichael felt sheerly bipolar impulses..."

éBack to the Table of Contents