I'm not certain that I like the idea of a ring being moble. The subject had been tossed into the "don't worry about it for now" section of my mind and was slated for eventual review.
Brainstorming for now:
Allowing a ring to be scribed on to a small object and a duration ring spell to be cast upon that ring will enable the creation of small enchanted devices with spontaineous magic. This maydevalue lesser enchanted devices and may also prove to be so useful that characters end up doing it frequently and as a recsult the stories told in your game could be stories of cheesy silliness as characters take advantage of "ring items" to do all sorts of things that would otherwise be more interesting.
Is there a downside to making rings stationary? I can imagine a magus who draws a ring on a rug having his spell destroyed when someone tugs on the edge of the rug which lies outside of the ring. I think that I can live with this. How about a ring that is scribed on the deck of a ship? Would it be destroyed when he ship moves? I find that prospect less easy to live with.
I believe that you can put the ring on an item without any trouble. Since it doens't say so in the RAW I would hpwever probably personally house rule it that moving said item would end the spell.
IMHO:
I think that the "feel" of magic is more important than technical minutia, otherwise parma would be unusable, and ring magic certainly feels like it is meant to be immobile, because the ring is meant to define an area, not just be a circle.
As far as a ring on a ship, I would allow it, as it is defining a small area in a structure. That feels right. Otherwise you would not be able to do ring magic on a flying castle either. Perhaps the rule of thumb could be rings must be defined on a surface upon which the target would stand. This might rule out putting a ring spell in the rim of a cookie jar to catch greedy children, or an ever-burning brazier.
A ring on a rug is not much different than a ring of chain which I think a major NPC in Guardians of the Forest uses. Both are very fragile and easily disturbed. Moving the rug may end the spell.
Rings are, in large part, based on summoning/protective pentacles and other such images, both out of historical sources and fictional ones. Some imprison, some hedge out, some act as portals, others do one thing or another. Depending on the world, some pentacles can be placed on rings, or medallions, or tatoos, or other quite portable items. In Ars, any of those could work, or be adapted.
However, while as a reader and fan of fiction I find those flights of imagination quite enjoyable to read/watch, as a Story Teller I find the potential quite disturbing, and likewise as a Player in such a world. I, personally, do not think that opening that particular door is a "good plan", for while it allows some nifty gimmicks, it also points the way to several absolute monsters.
If you want to include it, keep it in the NPC/BBEG realm, of those effects that do not mesh well (ie, AT ALL!) with Hermetic Magic. If a Player wants their character to abandon their study of Magical Theory and pursue some other teachings, then why are they playing Ars?
A question came up in a game I play in whether rings can be inscribed on a wall or ceiling, and the spell being targeted on an object within the boundaries of that circle, like a torch hook. Part of the problem for me is that long term ring spells need to be somewhere were they wont be smudged, and putting it on a coin means if you pick up that coin it will be smudged. You shouldn't have the ring made out of a non smudging paint or chalk.
But then I consider the question of what kind of a surface can you inscribe a ring on. A cracked wooden surface which is irregular and has gaps? A rock surface with thin fissures running through it? How smooth and consistant must the surface be to take a drawing for a ring.
That then brings up the question of what kind of tracing or drawing of a line is allowed for a ring. I think carving is out as it must be done by the magus during the casting of the spell. A band or a chain can be laid on top of a surface, but that by it's nature is flawed as it can easily be moved and disrupted. Paint and chalk has no problems. I think impermance is the key.
I have to disagree. The rules specifically state that you can trace a pre-existing ring when casting the spell. And the option I had proposed was inscribing or etching the ring into the surface of the disc. We're talking about cutting a circle into the metal - this is not likely to be damaged in any way by normal handling.
I can see the argument about movement of the ring after casting causing the spell to fail as the ring delineates a hermetic space. But I'd rather it be consistent. Either it must be stationary (e.g. no ships or wagons) or it works everywhere. I'm not happy with a rule containing special cases.
As for the other part - I would be fine with a ring laid vertically or on a ceiling. And I believe it's stated somewhere (faq on redcap, errata, or in the rules) that the circle / ring doesn't have to be geometerically perfect. As long as it's roughly ring shaped, it will serve. So that suggests to me that even a warped or splintered board would work initially. It would be bloody dangerous as it would likely fail at some point because of additional warping or splintering. But that's just my opinion.
Ships have long been a strange situation. While nothing on them moves in relation to each other, they are, in fact, constantly in motion, even while at dock (rocking, rising with the tide, etc.)
So, in fact, any spell that is not movable but has a duration more than "instant", when cast on a ship, will be "left behind" as it moves forward. And if the ship is moving quickly, any spell that cannot be moved at more than a fast walk (6+ mph/10+ kph) is left behind. Create a non-mobile illusion, and it slides back on the deck. Animate a sword, and it needs to be constantly moved forward just to "stay in place". Levitate, and watch the ship slip away beneath you. Rego a person into place in the hold for a day, and first, as the tide rises, his legs are crushed, then later his neck broken as it drops again. And so on.
There is no easy solution to this problematic mental paradigm - either you use one, or the other. Some SG's wink at it, some just forget, some enforce it (and shipboard magic becomes that much more difficult)- to each their own.
Shipboard rings (or on wagons, or whatever) fall into the same discussion- there is no right or wrong, only what you are comfortable playing. There are pros and cons for each. Just be consistent.
And you can be consistent and still have some interesting story options. Personally I am in the "moving-a-Ring-spell's-circle-ends-the-magic-camp" but if travelling this only makes the challenge of having other spells to keep the ship in place while you have to use a Ring or Circle spell. Or the sailers might have their fuss with a magus that demand the ship be firmly grounded!
Perhaps we can fix this with something along the lines of the following:
Magic is based on the magus' frame of reference. Any spell mentioned above would work as intended, as long as the frame of reference the magus held at casting was appropriate. It is not difficult to stand aboard a ship and percieve the ship as the structure upon which you stand, which would effectivly define the ship as stationary for the purposes of the spell. Perhaps in such a situation, the magus would be required to make a concentration check to keep his preferred frame of reference in mind while casting if there is more than one frame to choose from (the deck of a ship or the sea). Casting a levitation spell (no horizontal motion) on a ship could either keep you floating motionless in relation to the ship or the sea, but not both. I do think that the violent motion of a ship in a storm would possibly screw up the spell, but as long as the ship was moving in a reasonably stable fashion, you would be ok.
This would rule out casting ring spells on a finger-ring and having a permanent rule-abusing flashlight.
I know relativity is not a very Mythic Europe-like concept, but Bonisagus was the Einstein of his time!
I worry that would work better in theory than practice.
The problem (as so often the case) is "where to draw the line?"
If a circle on a wagon is acceptable, what of on a cart? Large merchant's Handcart? Wheelbarrow? A saddle, surely- any good horseman knows his horse is his frame of reference...
I know what you're saying, and the image of a ship is a strong argument, but when does the ship become a canoe, and then just a floating log?
The only practical answer may be that ol' "SG discretion". Case by case, you have to rule, and your players trust you to be fair and consistent. Good luck on that.
As far as I can tell from the guidelines and examples, spells and item effects are movable by default. There is no extra cost or special treatment for magic that travels along with the caster or target.
