Fine tuning Invisibility spells

Call to the lab rats :smiley:

I have been lurking on this forum since a while and playing Ars since... well, since 2nd edition (ho boys, my bones are creaking, 'm feeling old). This is my first question.

I have a Imaginem specialist who is trying to develop a few improved invisibility spells to travel unseen. He cheerish very much is quiet life and is extra careful (probably too much) to protect his privacy. Also, he is not very practical or pragmatic so his spells are not always optimised.

It has been established in this topic (The Invisible ship) that spell granting invisibility to a structure, grants by default invisibility to its contents, creatures included. However, it is not specified that people which are turned invisible can see each other or, for that matter, anything within the structure. So short of any supernatural ability or adequate spells, they cannot really interact efficiently with the structure or its content (behaving somehow like blind people), right ?

Would an Intellego requisit (and an increase of +1 magnitude) solve this problem, by granting everybody present the ability to see what this spell turned invisible (and only this spell, it does not grant "See the Invisible") ?

Second question: turning a carriage or a small boat invisible
PeIm 20 makes on person invisible, +2 magnitude to increase target size to Room (so PeIm30) is it enough for a small boat (dinghy type) or a carriage ?

Third question: turning a building invisible, but not its habitants
Again, based on PeIm 20 +3 magnitude to structure (PeIm 35). This normally would turn a building and its content invisible. If the magus only wants to turn invisible the house itself, its content, but not its occupants should it increase the magnitude by +1 for higher control ?
My magus could see this spell as quite efficient to find intruders (yes, there are other spells to do that, but 1) he is not very practical - not that it dawned to him, 2) it bypasses any magical protection 3) yes, it will violate the privacy of sanctum, but did I mention he was not very thorough in his thinking process ?), or as a way to confuse people in their own building: they cannot see walls, closed doors, fire place and so on.
It has also other practical applications, like any sight spell becomes suddently more efficient, but it is more his sodales that will find that out.

I would probably buy that.

Room affects whatever is inside the Room. If you just want the boat or carriage itself to be invisible, add a magnitude or 2 for size.
But if you want to make the (transport) and it's contents invisible, I'd go with Structure, simply because it includes the structure itself.

Errr. maybe? Probably?
Never thought about that one before.


Could that be covered by T: Part? for just the area you want of the structure.

It kinda could, except we alread want T: Structure. So T: Part is either redundant or the equivalent of "+1 fancy effect".

My view was that a building is a many time bigger than a man, so I found hard to believe that "Part", which is only one magnitude higher than "Individual" would be enough to turn invisible a building. Just for the sheer volume, I would go with Structure.
Where I am not sure is if making a building invisible or making a building and its content invisible deserve a different magnitude. Both spell could be of the same magnitude, except than within the spell design, the restriction to affect only the building itself is embedded in the spell (I am insisting on "embedded" because I do not believe a single spell should be able to do both and let the magus choose on casting).

Welcome to the [strike]killing floor[/strike] party! :wink:

Correct - all "sight" imagonem has been destroyed, so nothing yields anything for the eyes to see.

Possibly, but it could(?) set a bad precedent to simply hand-wave it with no regard to the effect being added.

When a spell does double-duty like this (here, both PeIm and InIm), it's best to base the effect off the higher of the two Base values for the two (or more) effects being combined. We know that PeCo "invis + motion" is Base 5, but InIm varies, depending on the exact nature of the effect (see InIm Discern the Images of Truth and Falsehood, p 144, and Discern Own Illusions, p 145). The latter would be only Base 1, so simply adding +1 magnitude for "additional Art" would cover that.


That's only for the Caster. Giving a group of people a "magical sense" is more challenging, as described on page 114, col i, top.

So - if you want to ignore the rules, yeah, +1 magnitude is fine. But if you want to keep the rules in mind, it's more complex than that. (But that's for all invisibility, so that doesn't mean that you can't just rule "+X magnitudes, done, leave me alone" and go on with the game - that certainly works too!)

The important thing is not to be slavish to the rules, but to 1) understand when and how you are tweaking the rules so 2) Hermetic magic in the Saga has enough consistency for your Troupe. :wink:

(Would this then be easily applicable to any PeIm T:Group effect, to allow an invivisble party to see each other? If not, why not?!)

However, I'll also toss this out - there are 4 basic ways to "be invisible" in genre, each taking an additional leap of imagination. The 1st is to simply allow light to pass thru the object - the movie "The Invisible Man" falls into this category. The 3rd is to destroy the "species" coming from the object - this is the default AM PeIm model. The 4th involves mental effects of one sort of another - "It's all (not) in your mind".

The 2nd (which I intentionally skipped) involves bending light around the target - this is "the Philadephia Experiment" model. If you used Rego Imagonem to somehow do this, you would only be "invisible from the outside" - this could, possibly, solve the problem.

Exactly. You aren't changing the Target to a higher category, you're staying with T:Individual but bumping the size of that Individual to something above the Base "individual" size allowed for that Form (which, for Imagonem, is ~1 human). +1 Magnitude = x10 individuals equivalence, so enough for a carriage or small boat. See insert page 113, "Targets & Sizes".

But Target:Structure would do the job as well, regardless of size.

Here you are bumping into Bonisagus himself, and the Hermetic model he established and "we" have inherited. This is exactly why The Order is unpopular with many Hedge Wizards, and exactly why they are able to trade spells so freely - because "left field" Targets like this are not incorporated into the default tools Hermetic magi have been given to work with.

Understand the diff between T:Individual and the size of the Target, and those in relation to the definition of "Individual" found in the short Intro to each Form in the Spells section. Read that insert on page 113.

You'd either need to either 1) use T:Part and additional magnitudes for Size, or 2) simply define what is/is not made invisible by the spell (quite possibly with +Magnitude(s) for "fine tuning" and go about your business).

In all these situations, also see The Central Rule, page 111.

One caveat for all this. Warping! Lots and lots of Warping! Almost any spell that makes more than one person invisible will grant a Warping Point every time it's activated/used (except for the magus casting the spell), thanks to it being a powerful effect (6th magnitude).

As for walls and such, Part target is your friend. You no longer care how big something is, part target will let you have some effect regardless.

What you are probably looking for, with your castle, is a kind of shell at the boundary that destroys species moving outwards from the castle. Problem is, the only guidelines is Base 4 Destroy an object's ability to affect sight. That makes it a bit harder to create the effect you are looking for.

Personally, I would start from that Base 4 guideline, then add a magnitude or two for a "shell" effect. I don't hink an Intellego requisite is really necessary, as the spell would specify that it destroys the species leaving the shell (as established by the Structure's boundary).

So as a spell, you'd get a level 45 spell (Base 4, +1 Touch, +3 Moon, +3 Struct, +2 complexity).

Just MHO.

Bending light would be Ignem rather than Imaginem.

In the Ars paradigm, you think so?

I see the "light" of Ignem as more "illumination", not the sensory data that emanate from an object allowing it to be seen.

And I know it gets fuzzy in places - does an illusion of a lantern shed any light at night, and if so how far away can you see by that light, and if not how can you see it from far away? etc. etc. Discussions for magi with Potent Philosophiae. :wink:

It's actually quite clear in the rules: You can't affect "light" without an ignem requisite. Hence invisibility not removing your shadow. So an illusion of a torch only sheds light if you add an ignem req.

But altering the direction of propagation of species is pure rego imaginem, even if in the real world that would be bending light.

Yes - as Kingreaper says, the Rules go into more detail in the Jerbiton chapter of HoH:TL (page 61 onwards). Essentially, species are emitted by an object, and then carried via a medium. In the case of visual species, that medium is light. So for example, in a pitch black room, an object will still shed species, but they won't be able to get to your eyes because there's no light to carry them there.

But yes, you could also manipulate the path of the species directly using Rego Imaginem, rather than manipulating the light carrying them. You'd still need to do something about the species from the thing you were trying to make invisible, even if it's just warding it against light whilst making the species from behind it pass around it.

Thanks all for your answers.

To sum up:
Turning a building invisible (and its inhabitants) for a day: PeIm35 (as I initially thought), simply because PeIm 20 is Ind; Sun; Contact and bumping up to Structure add +3 magnitude - up to here, everybody agrees.

Letting people inside the building see each other and the building, there is a little bit of debate. The most canonical way would be to design a spell granting "See through my own illusion" bumped up to Structure, so all inhabitants can see the illusion. But it is not unreasonable although not canonical to solve the problem by adding Intellego requisit, thus adding a magnitude.

Turning a only a building invisible will be PeIm20 +1 to bump Ind to Part, +2 for the size increase, duration and range remaining unchanged (Touch, Sun) - which seems the most canonical way to approach the problem, although other have propose alternative solutions. Since other solutions seems to agree with a spell level between 30 to 40, so I am quite happy to set it at 35 - it feels about right.

It was one point I overlooked. Would it still be the case for an effect lasting a day or less ? As I see it, whether it is a building or a carriage my magus is making invisible, it will only be for short period of time: when travelling for the carriage (and then, only if there is a risk to be seen) or for a special occasion in the case of a building.

By canon, that alone would not do it. That, alone, would only grant the Caster the ability to see their own illusions - and others do not share that ownership. By the rules for granting magical senses to a group of others (p 114), Muto Mentem is required w/ the approp InFo as a requisite - a hefty effect indeed.

Which is why a casual "+1 magnitude" may be seen as a gift to the mage/player designing this spell, and the troupe as a whole if the precedent is carried over.

If the effect is a "powerful mystical effect" (roughly defined as 6th magnitude or higher, see p 168 col i), it can be D:Momentary and still cause Warping.

I do not agree here with the need to develop a Muto Mentem as I want to extend a spell from self to contact (I do not grant Second Sight or other generic abilities), for a very narrow range of spells that are casted by the same magus.

But I was hasty in simply bumping the area of effect: I would need to increase the range from self to contact and the area from Ind to group +1 or 2 magnitude (to increase from 10 to 100 or 1000 people - which should be enough). I am aware that the initial spell has a range of Vision, but is designed for a single user, hence the magnitude increase.

So in this case the magus would be granting ability to see through its own illusions in everybody inside the structure (that the magus would need to touch). So a total increase of +4/+5 magnitude on the InIm 15 to see through his own illusion, which still bring the total level around 35 or 40. I understand that hand waving the solution by just adding an Intellego requisit and a +1 magnitude increase might not suit all playstyle. But since my players are not too keen on splitting hair and going into the nitty gritty details of magic theory, species and so on, I will pick up this solution and live with the consequences 8) for future spells development.

One way to get around the 'we can't see each other' problem is to employ non Imaginem intellego magics. Spells that allow you to perceive heat sources or feel the boundaries of air or sense the presence of people can mitigate some of the difficulties. And it's possible to keep these spells below the 6th magnitude, so it would be a matter of casting several spells on each person (an invisibility and a sense spell). Not practical for a home defense strategy, but for traveling safely it would probably work very well.