Dominus demonstrates that the value of a mnemonic is in the mind of the beholder (and that not all mnemonics are simple), as one person's mnemonic can be another person's complex chain of deductions:

I just remember that the terminator on the moon always goes from right to left. For some reason I've never had any trouble with that.

However, I used to have trouble remembering which way to turn screws and faucets, until I invented a mnemonic: COUNTER-clockwise to UN-screw. That adresses the screws directly, and because I understand how faucets and other similar devices work, it solves the faucet problem also. I imagine the faucet mechanism in my mind, and it becomes obvious whether I should screw or unscrew; then I recite the mnemonic, and that tells me which way to turn it.

This sort of derived mnemonic, where I can deduce which way to go because I know how something works, can be Rube-Goldbergish. For example, I can never remember whether noon in Philadelphia is morning or afternoon in California. Invariably, I follow this chain of reasoning:

1. The sun rises in the east.
2. (Imagine earth floating in space with sun peeking over east rim.) Therefore, the Earth rotates from west to east.
3. Therefore, Philadelphia gets to the terminator before California.
4. Therefore, when it's noon in Philadelphia, California has to wait a while to get to noon.
5. Therefore, it's still morning in California.
6. Sometimes this goes one stage farther:

7. Since it gets earlier and earlier in the day as you go from east to west, and the international date line has to compensate for that, when you cross the IDL from east to west, you immediately get one day later.

And I really do start from the sun rising in the east, every time.

I use similar complex mnemonics to remember whether cyclones rotate clockwise or counterclockwise, starting with the fact that the sun rises in the east and that the earth is fatter at the equator than at the poles. You can deduce a startling amount about the weather if you start with those two facts, plus `hot air is lighter than cold air'.

For some reason, I've never had any trouble remembering the difference between clockwise and counterclockwise, although to this day I confuse left and right. The physical mnemonic of holding up my hands, index fingers and thumbs spread, to see which one says `L', is still occasionally helpful to me here.

Other mnemonics of this type include the famous `right-hand rule' (actually a convention rather than a rule) and one I heard lately for the number of days in each month, where you make two fists, and January is your left little knuckle, February the space between the little and fourth knuckles, March the fourth knuckle, etc. Long months are knuckles and short months are spaces between.

Comment from Jed: I can't believe I left out the knuckles one; it's my favorite mnemonic, and I use it all the time. Note that you ignore the thumbs; the two index knuckles are considered adjacent, with no dent between them. And you run out of months before you run out of knuckles. Anyway, Dominus proceeds to digress into a discussion of finger names:

I'd be interested to learn which languages have names for the individual fingers. In English, the names are very bizarre indeed. Starting with the thumb:

1. Thumb
2. Index, pointer, first
3. Middle
4. Fourth, ring
5. Little, pinky

There are at least two interesting points: 1: The numbering is inconsistent, since there is only one finger between your first finger and your fourth finger. Apparently when you get far enough from the thumb, it starts to look like a finger itself, but up close it is a different object. [:-)] 2: There is a `little' finger, but no `big' finger, even though the middle finger is an obvious choice for the `big' finger.

(`Index' is Latin for `pointer'; see `index', `indicate', etc.)

Daylight Savings Time begins the first Sunday in April, ends the last Sunday in October. As system administrator, it's my job to know this.

(Other comments on Daylight Savings Time elided.) Whewâ€”big comments. My only immediate response is that maybe I should become a system administrator so I'd be able to remember when DST starts... (I too have Rube Goldberg figure-it-out-step-by-step mnemonics, but I can't think what they are at the moment.)

In other commentary, Kendra checks in with this:

As a young Latin student the most helpful mnemonic device I ever learned was "Can Queen Victoria eat cold apple pie?" for the 7 hills of Rome: Capitoline, Quirinal, Viminal, Esquiline, Caelian, Aventine, Palatine. I also still sing the fifth declension endings to the "Battle Hymn of the Republic," but I'm not sure that's really a mnemonic.

For the most part, though, I found mnemonics pretty unhelpful: seemed like they were just one more thing to remember.

When I took Biology in the 9th grade they told us that King Philipp came over from Germany swimming. I feel gypped.

Nancy Curtis suggests a mnemonic I'd never heard before for the lines of the bass clef, bottom to top: Good Boys Do Fine Always. As she points out, "[t]he real problem is remembering which mnemonic goes with which clef."

She also provides a great mnemonic for the seven layers of the OSI Reference Model for computer networking: All People Standing Totally Naked Don't Perspire. (Application, Presentation, Session, Transport, Network, Data-Link, Physical.)

Dominus offers another conceptual mnemonic. He says he used to have a hard time remembering that "[i]f an object floats, it displaces water equal to its mass. But if it sinks, it displaces water equal to its volume." Eventually someone told him: "Think of a pebble, made of neutronium. It's small, but it weighs a lot. If it were to displace water equal to its mass, then when you threw this little pebble into a swmiming pool, ALL the water would have to jump out of the swimming pool. So it must only displace water equal to its volume."

(Last updated: 3 June 1997)

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