I had an idea for a spell but i'm not sure whether it would work given ME physics.
The Instant Conflagration.
This nasty spell turns all the air in a room into fire. Quite aside from the damage from the fire, this also removes air from the room. In shoddily built house this might collapse the room. In other instances the sudden violent move of air back into the room may break doors, fling people off their feet and hurl furniture about. The fire itself is gone almost as quick as it arrived so only very flammable materials are likely to burn. +5 fire damage to anyone in the room and possibly physical damage depending on the surroundings. (base 4, +1 touch, +2 room)
Basically it works like a fuel air bomb, it burns off all the air creating a vacuum. When the air surrounding the area rushes in to replace that burnt off, it causes huge amounts of damage.
So what do you think, would it work hermetically or not?
We had a similar version for 4th called "Miller's Bane", around level 20. It created a cloud of finely ground flour, but did nothing to ignite it, just disperse it, which would be considered a very precise effect in 5th. I haven't taken the time to rebuild it for 5th, there being some dispute over how much flour can be created at the base level...
I believe we had the +5 damage as well, though we covered a fairly large area with it...
Why flour? Mills, throughout history, have been known to explode with little or no warning. What would stop a magus investigating why their mill suddenly exploded from duplicating the effect?
The spell had a secondary usage - once the flour settled to the ground, it was a great way to find where invisible things were...
Given that we are talking about mythic conceptualisations and practices here (albeit within the MP), I would adopt a more flexible approach to the question I think.
Given that the idea of vacuums existed as far back as Plato (notwithstanding his rejection of the concept) one could argue that a Hermetic mind might well embrace and advance notions otherwise ridiculed or shunned (for philosophical or religious reasons) by contemporary mundane society.
There is a brief but interesting summary of historic understanding in this Wiki article...
If I had to decide I would say that within the OoH many undesirable notions exist (magic in its various forms and branches being a paramount example of this). Thus, sure it would not be absolutely inconceivable to a magus that the sudden consumption of air in a closed space would result in a rapid influx of air to fill the void. After all, the ancient Greek philosophers themselves gave rise to the widespread and long-running notion that "nature abhorrs a vacuum" (regardless of the faulty assertions that led them to make).
The final decision, as ever, rests with your SG, but if he/she would need more convincing than the explanation offered then I would suggest requiring creating the spell through experimentation. This would mean possibly taking more than one season to accomplish and thus satisfying any doubt that the idea had been thoroughly tested in the lab first.
While I agree with Boxer that in principle the concept of a vaccum was present, I don't like the spell's smell. It's too modern. If pressed for an explanation why, I would suggest that fire is an element, not a vaccum. When you replace the air with fire, it's like replacing it with some other gas - not a vaccum. I would therefore suggest a more fiery effect, lasting longer and doing more damage, but not a vaccum effect.
I concur with YR7. Paradigm calls fire an element, so you wouldn't have any rushing of air back in, it would just be a shift in state from air to fire. When the duration concluded, the fire would just revert to being air, but fires started from the magically created flame would continue to burn.
Now, if you included a rego aspect to pull more air in, that might create the effect you want...
Ummm, sorry lads but I really have to disagree with you here.
True, the MP considered fire to be an element, which is about as true as Plato's insistence that vacuums could not possibly exist. Simple fact is, MP or not, the sudden consumption of air in a tightly closed space WILL create a vacuum and thus a subsequent differential in external and internal pressure that WILL seek to equilibrate with great force.
The MP itself is only a measure of WHAT the common man of the time understands as to the nature of the world around him, not what truly IS. It cannot suspend or otherwise negate the actual laws of physics even if those laws are not yet comprehended as such.
I would certainly rule that the resulting effect might not be understood in terms we now commonly accept as scientific fact, and likely the whole process would be described as a battle between the elements or somesuch.
After all, we can be mythic and magical without disregarding fundamental properties of nature.
Bzzt. That's where we'll have to agree to disagree. Whatever physical laws we know today that were unknown to the medieval-or-earlier world actually do not exist in mythic europe. Things (tm) work differently in that mythic world over there.
But debating this is unlikely to sway anyone from his or her views, so let's stop there
Yup. for instance, matter can be created and destroyed in ME. No need for the MC2E equation to hold any validity
In ME, fire does not consume air. The air in the room is transfoprmed into fire for the duration of the spell. Then, it turns back to be perfectly fine air filling the room.
IN fact, if you transformed all the air into fire, according to real physics, the fire would not even spark, since fire does not exist without air; no air (transformed to fire) means no fire either in the room Sounds silly for magic, isn't it?
Touche, quite true. However it's more the principle than the particulars of the spell description itself that I am arguing. To be truly consistent one could just as easily suggest a PeAu spell in a closed room which WOULD negate all the air and leave nothing (vacuum) in its wake.
Actually, PeAu would create a Vacuum. I doubt it would make the entering of extra air an explosive/damaging effect. I see it more like the room being refilled in a few rounds (and everybody there losing 2-3 fatigue levels in the meantime).
Remove the idea of modern physics from your mind: they do not exist in Mythic Europe: MC2E is false, evolution of species is false, cinetic movement is false.... etc etc. It is magic. Enjoy!
So, regarding the spell: I would make it cause +5 or +10 damage to everybody, and then things turn to normal. No extra effects. Well, appart from the charred room and burned out stuff, that is
It doesn't create a vacuum, it creates flame, which itself exerts a pressure on its surroundings. This is why, when you light a natural fire, the atmosphere doesn't squash the flames into nothing. If you convert air into an equal volume of flame (as per Lungs of the Fish) it will exert the same pressure as the air it replaced, because flames naturally have the same pressure as the surrounding medium. If the fire persists, it will cool down and contract, but not instantly. If you convert air into an equal mass of flame (as per Trapping the Fire) it will exert a much greater pressure, because it is much hotter. After the ensuing explosion, the fire would turn back to air, creating a partial vacuum. The overall effect would be similar to an FAE - and worthy of a munchkin.
Generally, I believe Muto should turn one element to an equal volume of another. Changing all the air in a room to stone should fill it with solid rock, rather than making some pebbles and leaving the rest as a vacuum. Changing all the air in a room to water should produce a room full to the ceiling with water, which will burst the walls of a typical building, though some castles might be as strong as dams. Changing the air to fire should produce enough flame to fill the room, and no more. The flames will try to fly upwards, out of the windows etc., seeking their natural position. The situation is much the same as an ordinary house fire, but lit and extinguished unusually quickly.
A level 3 base PeAu spell/effect would indeed merely result in bad air (use of the term "create" in reference to a Pe spell/effect is somehwat of an oxymoron), but level 4 according to the PeAu guidelines reads "destroy still air" which to my mind is significantly more than a reduction in quality, more of a total negation (however momentary that might be).
Wasn't there once an peAu spell to destroy air around a magus? Jupiter's Resounding Blow or something? It was a 4th ed thing, and perhaps in WGRE. I'll look it up, when I get home.
Anyway, if PeAu destroyrs a volume of air, IMHO the empty space is instantly filled with new air, of same properties as the surrounding air, with little side effect, other than rushing of air. So destroying air around a person should perhapos cause the difficulties in breathing, and they'd feel the air rushing in. But no explosive decompression of the target, from being in vacuum for a short while, nor some explosive or crushing effect of air rushing in.
But did the ArM Physics actually know that fire needed air to burn? Did somebody put an inverted glass over a candle, and saw the flame go out after some time? And did they jump to the logical conclusion, that fire needs some air to burn, and once used, the fire goes out? Has somebodu been inside a burning house, and thought the air was being consumed, and that this was causing the shortness of breath, or did they just think it was the smoke.
BTW As far as I know about FAEs, they're caused by having a combustible liquid or gas under high pressure, suddenly release it so it mixes in a favourable ratio with the oxygene in the atmosphere, resulting in an explosion much surpassing conventional explosives. Early experiments used coal dust, and was thought up as a way of clearing mine fields, but it couldn't have worked very well, otherwise it would have been more wdely used. This is IMHO not the same as a MuAu/Ig spell to transform air into fire. Doing this would make a fire, which fills the entire target area (barring the air in somebody's lungs, since this should require a Co req.). There is only burning, no explosive effect. And I agree completely with previous posters, feeling that the fire would turn back to air after expiry of the spell. It would not create a vacuum and no explosive air wave, or no back draft when new air rushes to the mundane fires, created by the magical one.
(Forgive me for the following, but the term "fire" can pertain both to the substance and to the element. The former is made principally from the latter, but also contains the elements of air, earth, and water.)
Certainly one view was that fire-the-element had a strong attractive force, which is to say that it attracted other atoms of fire to it. Thus fire- the-substance - which has a high abundance of fire-the-element - attracts more atoms of fire-the-element from the substances around it, such as the air and the fuel. Once it ceases to be able to grow (i.e. the surrounding substances have relinquished what fiery atoms they can) then the flame loses its form and ceases to be a substance.
So, under the paradigm of the day, fire does not need air to burn. However, it does need the atoms of fire-the-element that are part of air-the-substance to continue its existence.