Hello
I read the description of this spell (HOH S p63), but i can't understand what it is useful to; can someone help me?
Thanks
It disintergrates things. It turns a thing into optic species, which then scatter as they normally do, with the speed optic species normally have, so that when they turn back the object is basically dust scattered around a several mile radius.
(If I am remembering correctly: noble's parma).
Argh, i have to say i don't want exactly the advantage (per example in face of a basic invisibility spell)... can some lights be provided to me? 
Exar.
If I'm recalling the spell coreectly Scattering Like Light is an offensive spell, and what it does it takes a target and turns it into very fine dust over a radius of several miles. Its superiority to an invisibility spell is that it destroys things and an invisibility spell just makes them invisible. The point you seem to be missing is that when a thing is turned into species, passing light scatters these species, so the object loses all coherence above an atomic level and is scattered like dust.
I never noticed this spell before. It's listed as a MuTe(Im) with duration Mom. Wouldn't the target just phase out for an instant and just phase back in? I don't see the point of a momentary disintegration effect. You can't use momentary muto for permanent effects.
Well, one analogy of this spell that may help you think about it is a MuCo(Te) spell cast at a person standing in a rapidly flowing stream of water, that converted them for a moment to sand. During that moment, the rushing water will displace much of the sand and the poor target is going to reform with bits of himself downriver.
Of course, light strikes every part of the target at the same time and seems to carry species much faster than a river carries sand. So being converted, even for a moment, to species means the target is instantly blasted and carried away by light. If the resulting species are not somehow contained (being within an enclosed space, or other imaginem magics are in play) then when it reforms a moment later, it is reduced to essentially extremely fine dust.
It sounds along the same lines of "I Muto his blood to quicksilver and he dies of mercury poisoning". It seems against the spirit of the guidelines.
MoH has a MuTe momentary spell that turns a metal object momentarily to sand. The magi who invented it is a muto specialist who mastered it for fast casting. He uses it as a defensive spell. You swing at him with a sword. He transforms it into sand momentarily. It’s now little bits of metel scattered all over the floor.
Think of it like Rock of Viscid Clay ArM5 p. 154. That spell turns rock to clay, which can then be manipulated as clay, not stone. When the spell passes the clay returns to being stone. This way you could hack through a stone wall with an ax (or a shovel). When the spell expires, the material you have hacked away doesn't fly back into the hole and merge into solid stone agian as if the spell had never been cast.
Muto cannot kill a person directly, i.e. a MuCo effect that changes a living body into a dead one. That's Perdo. But muto can do essentially "direct damage" by changing either the target or the environment. Changing the air around a target to acid. Changing their clothes to raging fires. MuCo(An) can even kill by replacing your air breathing lungs with fish lungs. Likewise, a MuCo(Aq) T:part spell may be able to convert a target's blood to poison or acid with the usual effect of exposure to that much poison. I think some SG's will allow the last effect, others will not. But making a person unsuitable for his environment (like being composed of species) is a canonical way to harm someone with Muto.
So this spell doesnt work if its dark then?
I hear what you guys are saying but if disintegration isn't Perdo I don't know what is. I would never allow Muto to expand that far, species theory or no.
I'll defer to the experts on the board, but I understood that species are only carried by light. so if there is no light the species would just sit, immobile.
For some reason, it seems more coherent that species are always emitted. Otherwise mirror and transparent become hard to explain. You don't see anything in the dark because all iconic species look the same when they are dark.
But I don't know how medieval academicians saw it.
No, because in that instant, the species act as species normally do.
If you a person in to dust and put them next to a big fan, whne they rturn back, they are mince, not a person. Similarly if you turn an object into species and put them near a light source, the light blows the species away and scatters them, so that when the object turns back, it's just dust.
Perfectly dark? No it doesn't. It needs light to fuel the scattering process.
Your choice, of course, but if you transform a door into smoek, in your game, does the smoke turn back into a door in the same location once the Duration ends? This is exactly the same, IMO.
I'd allow that spell, remembering the rule that says that instant death spells have a minimum level.
Scattering like light is a Terram spell: you can't use it on people. IMC, a version to be used on humans would have to be level 40 or more, because all instant death spells are level 40 or more.
OKay now i begin to understand what it does...
It was difficult because IOS muto is the least useful of the arts ^^.
I agree your example makes it sound a little silly, but this is actually probably what I'd do. Muto is the art that works the least logical and most "magical" way, so things return to their original state when the magic ends. Otherwise it's too trivial to duplicate Perdo ("I turn the castle to smoke on a windy day") or Rego ("I turn the gold to water and let it drip until gilds my statue") effects, which really seem against the spirit of time limited Muto.
It does sound like most people do it differently.
Can you point me to where the minimum level for instant death spell rule is? I don't ever remember seeing it, but its possible I've just overlooked it.