I found this Appendix N pseudoscience in A. Merritt’s 1918 book The Moon Pool:

My theory is that the moon rock is of some composition sensitive to the action of Moon rays; somewhat as the metal selenium is to sun rays. […] When the light strikes them they release the mechanism that opens the slab, just as you can open doors with sunlight by an ingenious arrangement of selenium-cells.

Now I didn’t know anything about selenium except vaguely that it’s probably an element. Maybe you know more than me. Maybe you know that it was discovered in 1817, named after the moon, and used in light sensors from the 1870s until the 1970s. Maybe you know that its few commercial uses nowadays include glassblowing and as an ingredient in baby formula. Well, you’re very smart. I had to hit wikipedia to learn all that.

Here’s why selenium is a nice drop-in in a D&D game.

It sounds familiar and scientific, without having any specific connotations to most players (unless your players are all smarter than me too). It’s a little more technological-sounding than the traditional D&D magic materials (adamantium, mithril), and so it matches well with the strangely scientific bent that’s demonstrated by D&D dungeon builders, with their elevators, gas traps, and other automatic devices. Its use is an ancient secret of a bygone empire.

It’s steampunk. It was exciting during the Victorian era: Alexander Graham Bell used it in a photophone, which is a largely forgotten 1870’s version of fiberoptics, and it was still cool in 1918 when Merritt was writing. Like all great steampunk technologies, it’s been superseded by other technologies. (Silicon is a more efficient semiconductor, and polyvinylcarbazol a more efficient photoconductor, than selenium.)

It’s got a cool name. Selene is the Greek moon goddess’s name that also gave Selune her name. “Selenium” suggests some moonlight-drenched stone, maybe mined on the moon, maybe holy to its goddess, that calls to the heavens. It’s convenient that, in real life as in Merrit’s horror fantasy, it can be used to drive sun-powered (or moon-powered) devices.

OK, how do you use it in D&D?

In my last game session, the players captured a giant squid space ship, piloted by mind flayers, with a cargo of selenium in its belly. The PCs sold it to starfaring elves. The elves alloy it with mithril to make +1 mithril weapons. There’s a catch: selenium swords are sensitive to sunlight the same way drow weapons are, and they’re prone to damaging “sun rust”. (This is a further development of an idea I had before.

You could also use it the way selenium is used in real life, or in The Moon Pool, except magicked up: a selenium sensor can cast a spell under specific light conditions just the way a Magic Mouth can speak words under specific conditions. This ties into another idea I’ve blogged about, an electrum mirror, but with a different metal.

Selenium could be used to make magic items that only function in moonlight. A selenium sword that’s normal during the day and a +1 glowing sword in moonlight is a nice minor magic item that’ll be valuable to low-level characters.

Throw a pinch of selenium dust in the air and the light of a full moon shines down, even in a dark dungeon. This could be useful for banishing shadows, spotting werewolves, or summoning fairy creatures.

Real life selenium is poisonous, but I bet that D&D adventurers carry little vials of selenium powder (“moon dust”). A mouthful of this stuff turns you into a fey creature, which means you’re immune to charm and don’t need to sleep. You don’t need rest either: you’re immune to the effects of exhaustion for a full day. You can hustle all night and day if you have to. Over good roads, you might be able to cover 200 miles. Disadvantage: your blood runs thin. Every time you take an injury, you take 1d4 extra damage. Furthermore, after 24 hours, the exhaustion catches up to you.

“Fari! Duck!” Havilar cried. The second head slammed into her side and threw her into the lake. The icy water shocked her every nerve and she nearly gasped in surprise. The blue light of the water was all around her, and for a moment she couldn’t tell where the surface was and where the lake bottom lay. … She turned, trying to find some purchase, some touchstone that would point the way. And found herself facing a dark, jagged hole in the rock. … She ran her fingers over the freezing stone, the chiseled edges of runes still clear. No wonder it had been lost to the ages.
-Lesser Evils by Erin M Evans

It’s often a misstep that leads to a discovery. That’s quite common in adventure novels, and it’s a nice little encounter-design reminder: a dungeon can use a few easter-egg discoveries that can be found only by meticulous search OR by some sort of catastrophic failure. If everything goes well for the party, they’ll probably miss a treasure or two.

The most obvious example of this trope is the treasure or secret door at the bottom of a hidden pit. If you want to strip the idea to its most basic form, the very idea of a monster guarding treasure is central to D&D: you pass through a misfortune to get a reward.

More specifically, here are some situations where a creature’s successful attack reveals an otherwise well-hidden treasure.

Here are some 17th century historical figures with D&D names:

From Neal Stephenson’s Quicksilver:

On 16 August 1688, I met Liselotte von der Pfalz, Elisabeth Charlotte, duchesse d’Orleans, who is known to the French Court as Madame or La Palatine, and to her loved ones in Germany as the Knight of the Rustling Leaves, at the gate of a stable on her estate at St. Cloud on the Seine, just downstream of Paris.

This is a pretty awesome name for a semi-exiled, itinerant princess. It seems to have been the real nickname of Liselotte von der Pfalz. From her letters, it seems that she was a tomboy princess who preferred hunting to fancy-dress balls, and, as she says elsewhere, swords to dolls. It would be pretty easy to fit Lisolette, the Knight of Rustling Leaves, into any D&D campaign.

And how about this name? In a 1660 passage from his diary, Samuel Pepys mentions “Sir Harbottle Grimstone, Speaker for the House of Commons.” How about that name? It sounds almost aggressively, implausibly D&D, and I had to double-check that it was a real guy.

Neal Stephenson’s Baroque Cycle is about the era of Newton, Samuel Pepys and the foundation of the Royal Society: it’s the transition period where you’d stop using D&D to model contemporary scientific belief and start using d20 Modern. From the point of view of fantasy fans, periods like this are productive. As magic goes under the microscope, its formulae are recorded in lab notes.

Take this passage from Quicksilver, inspired by a real experiment conducted by the Royal Society:

Sir Robert Moray came to visit, and ground up a bit of the unicorn’s horn to make a powder, which he sprinkled in a ring, and placed a spider in the center of the ring. But the spider kept escaping. Moray pronounced the horn to be a fraud.

The description of this experiment, by which they prove that unicorn’s horn does not kill venomous beasts, raises some questions: where did they get the unicorn horn? Let’s put that aside. The D&D takeaway here is that, if magic does work, unicorn horns (and unicorns) should be very dangerous to venomous creatures. Let’s say that a touch from a unicorn horn forces a creature to make a save vs. its own poison or suffer its effects. A creature’s immunity to poison does not protect it against this effect. This is the sort of using-its-own-power-against-it magical judo you’d expect from a good-aligned creature like a unicorn.

Daniel… read the graffiti cut in the stone by prisoners of centuries past. Not your vulgar Newgate Prison graffiti–most of it was in Latin, big and solemn as gravestones, and there were astrological diagrams and runic incantations graven by imprisoned sorcerers.

One thing we know about the incantations of imprisoned sorcerers: none of them are Knock or Teleport. Here is one of the real Tower of London carvings, etched the sorcerer Hugh Draper in 1561:

It looks just like the kind of thing I doodle in meetings. In D&D terms, it actually looks less like a spell and more like a spellbook: something you’d carve once, and then consult while doing innumerable astrological readings.

The D&D inspiration I get from this carving: a spellbook is a collection of shortcuts and pre-computed values. A wizard can’t be permanently separated from his or her spellbook. Given enough time, the wizard can re-compute and re-draw the various calculations and diagrams necessary to cast spells, even with nothing to write with but a stone wall and a tiny piece of metal. I like to think that in 1562, after a year or so of turning his dungeon cell wall into a spellbook, Hugh Draper was able to memorize Teleport and get the hell out of the Tower.

Quag Keep is a bizarre book. It’s the first D&D novel (it was published in 1978, so it was written before Advanced Dungeons and Dragons came out). It’s by Andre Norton, an Appendix N author and a well-respected fantasy/sci fi writer, above the level of most licensed-setting writers. And yet it’s neither a great novel nor a great D&D book.

It seems to be based on a alternate-dimension version of Greyhawk D&D: there are many ideas that are quite interesting, but don’t appear anywhere else in D&D canon. Perhaps this can be explained by the book’s blurb:

“In 1976, Andre Norton was invited to play a new sort of adventure game, Dungeons & Dragons. Its creator, E Gary Gygax, introduced Norton to his world of Greyhawk. After a session of world building, role playing, and fantasy adventuring, Norton wrote “Quag Keep”, a tale of six adventurers from our world who journey to the city of Greyhawk in order to aid a wizard and unlock the secrets of the stronghold of “Quag Keep”.”

It makes a lot of sense that Andre wrote this after a session of D&D, not multiple sessions, and presumably without a lot of subsequent input from Gary.

The book is interesting as a piece of D&D history. It’s also interesting as a different take on D&D: a way D&D could have gone, had it taken a different branch in the road. Who knows, maybe it has some ideas worth bringing back into D&D canon.

I’ll read Quag Keep and look for its idiosyncrasies and see if I can figure out ways to use any of them in a game.

OK, here’s the basic premise: a bunch of real-world people get sucked into a game of D&D, where they are railroaded into an adventure via a geas. OK Go!

Boar helm, boar cloak-memories and knowledge Milo did not consciously search for arose. This other was a berserker, and one with skill enough to turn were-boar if he so desired.

1978 was well before the introduction of the Barbarian class, so the berserker here is either a Fighting Man or some unique pre-barbarian class. It seems like the latter, since at high level, the character gains the ability to turn into a were-boar. It’s an interesting idea for a class. I actually seem to remember reading something similar to this in an early piece of Dragon Magazine fiction, so maybe there was a fan-made Berserker class floating around somewhere.

Nor was he surprised that the stranger should have the pseudo-dragon as a traveling companion or pet, whichever their relationship might be. For the weres, like the elves and some others, could communicate with animals at will.

More details about the Berserker class! And also, incidentally, details about the elven race that you won’t find in the PHB: they can speak Animal.

This makes me think that it might be kind of cool to add a few languages to the usual D&D collection of Common, Goblin, Lawful Good, etc: maybe 5 or so animal language (Wolfish, spoken by mammal predators; Deer, spoken by mammal herbivores; Avian, spoken by birds; Piscian, fish; etc.) Let them be taken as bonus languages just like any other language. Maybe they would be restricted to “weres, elves and some others.”

The eternal war between Law and Chaos flared often in Greyhawk. It was in a manner of speaking a “free city”-since it had no one overlord to hold it firmly to his will. For that reason it had become a city of masterless men, a point from which many expeditions, privately conceived and planned for the despoiling of ancient treasures, would set out, having recruited the members from just such masterless men as Milo himself, or perhaps the berserker only an arm’s length away. But if those on the side of Law recruited here, so did the followers of Chaos. There were neutrals also, willing to join with either side for the sake of payment. But they were never to be wholly depended upon by any man who had intelligence, for they might betray one at the flip of a coin or the change of the wind itself.
…
As a swordsman Milo was vowed to Law. The berserker had more choice in such matters. But this place, under its odors of fresh and stale food, stank to Milo of Chaos.

As D&D has gone on, the importance of the battle between Law and Chaos has gradually diminished. in 1978, it was still a big thing. But the importance of the “eternal war” in Quag Keep is maybe even more important than it is in the OD&D rules. It’s explicitly a game-world concept, like race, not a meta-game concept like class or hit points. Furthermore, it’s a palpable thing: Milo can smell it.

Speaking of in-game concepts: as a “swordsman” (an OD&D level title for Fighting Men, right?) Milo is “sworn to Law.” It’s hard to say exactly what this means in QD&D (Quag Keep D&D), but it might mean that a) all Fighting Men are lawful and b) OD&D level titles aren’t metagame descriptors: they are the names of in-world military orders or ranks.

Berserkers, apparently, don’t have to be lawful: more evidence that they’re a separate class from Fighting Men.

“Deav Dyne, who puts his faith in the gods men make for themselves.” There was exasperation in the wizard’s voice as he spoke the name of the next. By his robe of gray, faced with white, Deav Dyne was a follower of Landron-of-the-Inner-Light and of the third rank.

Perhaps the most interest thing about Quag Keep is that nearly everything that I think of as a game-only concept turns out to be explicitly known by the characters in the novel. Deav Dyne is a third level (or rank) cleric. Furthermore, he wears a color-coded robe that shows that he is a third level cleric. When he advances to fourth level, he’ll get a new robe.

This makes it more plausible that Milo’s title of “swordsman” is also an identification of his character level. (Furthermore, later in the novel, someone says that Milo is “a swordsman, a rank that marks you as a seasoned fighting man.”)

The other interesting thing from this passage: Deav wears a robe. In QD&D, clerics are clothies.