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A battlemage practiced the art of close combat fighting, and could deal huge amounts of damage to his opponents at point blank range. He also had a special robe, which was enchanted by a powerful spell such that it parries all ballistic projectiles.

Unless the enemy attack completely overwhelm the battlemage in term of magical strength, the robe should survive unscathed.

I kept wondering why I still see battlemages getting wet in the rain? Wouldn't that imply that the robe can be dissolved by acid rain too?

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  • $\begingroup$ what material the robe made of ? if it usual cloth or fabric that can absorb water then thats probably the reason, though parry has a lot of meaning, but usually it more about blocking or stop the incoming strike and doesnt necessary mean deflecting or slipping it away or changing it to opposite direction, and maybe the robe designed like that due to your battlemage is a close combatant which seems like he will accumulate alot of heat and sweat... $\endgroup$ – Li Jun Mar 30 '20 at 5:27
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    $\begingroup$ I'm not sure why this is terribly different from a Kevlar vest or a suit of armor, both of which also block projectiles and get wet in the rain. $\endgroup$ – Nuclear Hoagie Mar 30 '20 at 13:29
  • $\begingroup$ This is kind of a dumb answer, but in the real world we have materials that are bulletproof but can get wet. Kevlar is an example. It's still a woven thing so water can get into it. You could say that the enchantment is on the threads to strengthen them instead of saying there is a "force field". $\endgroup$ – Captain Man Mar 30 '20 at 14:26
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    $\begingroup$ It's a little unclear in your question, but I want to point out that acid rain is not immediately dangerous. It takes prolonged exposure to do real damage. $\endgroup$ – Captain Man Mar 30 '20 at 14:48
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    $\begingroup$ The Germans are hunkered down waiting. They're coming. Into the village burst three M1A2 Abrams tanks. The Germans throw everything they have at it - the Fokker triplanes even score bomb hits. They don't even scratch the paint. even the hit marks are washed away by the rain. $\endgroup$ – Harper - Reinstate Monica Mar 30 '20 at 17:13

17 Answers 17

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The spell creates a force barrier that behaves like a non-Newtonian fluid.

A non-Newtonian fluid is a fluid that, among other things, increases its viscosity with increased shear force. This video shows examples of interactions with a non-Newtonian fluid. A protection spell applies such dilatant properties to the atmosphere around the wizard.

Ballistic projectiles have high mass and velocity. When they interact with the atmosphere in the region of the spell they apply a significant level of stress to the atmosphere. The spell's dilatant properties mean that such stress dramatically increases the atmosphere's viscosity and the projectile is stopped from passing through. By contrast, raindrops have a comparatively low mass and velocity and cause very little stress, and thus pass through with ease.

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    $\begingroup$ This is a very good answer. It also explains why if someone goes to pat the mage on their back, they don't loose their hand $\endgroup$ – Andrey Mar 30 '20 at 13:30
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    $\begingroup$ Not all nonnewtonian fluids act this way, se wikipedia article. Some increase some decrease and for some its more complex than that. Good answer, but want to clafify that it is e.g. a Shear thickening nonnewtion fluid $\endgroup$ – Lyndon White Mar 30 '20 at 15:48
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    $\begingroup$ This runs the risk of being very similar to the Holtzman fields in Dune $\endgroup$ – Dancrumb Mar 30 '20 at 16:02
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    $\begingroup$ If you're going to give a magic robe an explanation with real science backing, be ready to accept the other ramifications of it. For example, if rain moves slowly enough to pierce your magic cornstarch cloak then a wrist-snapped throwing knife moving the same speed should also get through. I recommend sticking to just magic answers like Marvin's. $\endgroup$ – user1717828 Mar 30 '20 at 17:02
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    $\begingroup$ Awesome answer. Around a mage there are a lot of things "non-Newtonian" ;-). Paradoxically, the non-Newtonian robe is still comparatively Newtonian (in the sense that it acts according to natural laws)! $\endgroup$ – Peter - Reinstate Monica Mar 31 '20 at 7:49
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The Devil is in the Details.

This hypothetical robe "parries all ballistic projectiles."

When rain strikes the robe it does its job, reducing the drops to zero velocity so that they do not penetrate. However, an unforeseen (and unwanted) side effect is that they are no longer ballistic in nature. As a result, the robe is now, for all intents and purposes, just a regular robe, and thus gets wet from the water that is in contact with it (the neutralized raindrops).

To answer your question, yes; the battlemage's robe (and by extension the battlemage) is vulnerable to liquid/shape-conforming attacks such as acid, boiling pitch/oil, drowning, and shaped explosive charges.

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    $\begingroup$ "Mage is here boyos! Swap out the boulders for pitch and acid" $\endgroup$ – Cireo Mar 30 '20 at 19:04
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    $\begingroup$ @JohnDvorak But pitch, damn, cover them, light them up. No force all cooking. Acid is harder to get for sure. $\endgroup$ – Erin Thursby Mar 30 '20 at 20:31
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    $\begingroup$ It's easier than you think to make lots of acid. Alchemists began making hydrochloric acid as early as the 1400s by mixing table salt and green vitriol. Both are common minerals that can be mined in bulk. Stored in glass vials, HCl can be contained indefinitely, but when a vial of concentrated HCl shatters it will rapidly evaporate into a caustic mist that is immediately agonizing on contact with the eyes, mouth, nose, lungs, etc. It's only sometimes fatal, but can easily cause permanent blindness and respiratory issues that would end the mage's career. $\endgroup$ – Nosajimiki Mar 31 '20 at 3:19
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    $\begingroup$ Why Acid? Boiling water is enough to cause damage. $\endgroup$ – kutschkem Mar 31 '20 at 9:04
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    $\begingroup$ @kutschkem, water doesn't stay boiling for long. $\endgroup$ – Pureferret Mar 31 '20 at 10:42
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The magical robe also magically perceives intent. Enemy projectiles? Blocked. Harmless raindrops falling from a benign sky? Come on through. Angry raindrops from an insulted deity? Blocked!

Additionally, this could optionally add a fun wrinkle where an "accidental" projectile, say friendly fire or a alchemical explosion, could actually become very deadly because there was no intent to harm.

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    $\begingroup$ I was going to say roughly the same thing, with an added wrinkle. The spell of protection is mostly passive... until it needs to block something. Then it needs to draw on additional magic from the wearer to do so. This means that one the wizard is exhausted (of magic), the robe will offer no further protection (until the wizard recovers). Since rain is not a threat, and there is a lot of it, the spell doesn't waste magic trying to block it. $\endgroup$ – Matthew Mar 30 '20 at 15:10
  • $\begingroup$ I prefer this to the many answers in the vein of "well, bulletproof vests can get wet" because it is more magical. Of course a magical robe should operate somewhat differently from a bulletproof vest. I'm sure that for most bulletproof vests, there's a particular type of acid that could be thrown on it to compromise it. Mages will have acid spells, so it is better if their robes can discern intent. This answer also opens up the possibility that perhaps a particularly clever mage could come up with an intent-shielding spell. $\endgroup$ – Zwuwdz Mar 30 '20 at 18:13
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    $\begingroup$ Intent, or effect; take your pick. A raindrop, particle of dust, or even an apple (thrown slowly) don't have enough energy to harm the wizard, so the spell doesn't waste magic deflecting them. This could allow clever ways to try to circumvent the protection (boiling hot water?) and wizards tweaking their protection spells to try to avoid such circumvention, which could add narrative depth. $\endgroup$ – Matthew Mar 30 '20 at 18:38
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    $\begingroup$ +1 for Angry Raindrops! >GRRRR-plop< $\endgroup$ – Criggie Apr 1 '20 at 2:52
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    $\begingroup$ I've actually been in what could be called "angry rain", because, yes, it hurt. And I'm not even talking about freezing rain or sleet. $\endgroup$ – computercarguy Apr 1 '20 at 19:54
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It's because you are looking at two different phenomena.

Anything gets wet because of capillary forces and surface tension.

Both phenomena have nothing to do with stopping ballistic projectiles.

It's like asking "why do I get wet though my sweater is pink?"

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    $\begingroup$ @Ryan_L how about "room temperature air is just molecule-sized bullets coming from all direction"? Keeping into account that the average speed of an oxygen molecule at room temperature is 483.5 m/s, the robe must deflect all the room temperature oxygen, so the wizard will die of suffocation (or by frozen nose/throat/lungs with the only molecules let forth being the cold ones) :grin: $\endgroup$ – Adrian Colomitchi Mar 30 '20 at 4:27
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    $\begingroup$ @Viki the robes that you are making from such materials fail to stop the "oxygen bullets". If they fail this, they can fail other kind of bullets too, including the "rain bullets" :grin: $\endgroup$ – Adrian Colomitchi Mar 30 '20 at 14:28
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    $\begingroup$ @AdrianColomitchi it sounds like the coat is just Maxwell's Demon in disguise. $\endgroup$ – Skyler Mar 30 '20 at 14:43
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    $\begingroup$ Many of these comments seem focused on velocity without giving any consideration to mass, inertia, or momentum which could be use to discern harmful from non-harmful projectiles.. $\endgroup$ – krb Mar 31 '20 at 1:37
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    $\begingroup$ @krb my point exactly. Clearly the spell must make some sort of distinction based on something otherwise, taking the consequences of no discrimination whatsoever between bullets and raindrops to the logical extreme, it follows the wizard will suffocate. Which means there's at least one degree of freedom allowing the spell to deflect the bullets but still get wet with raindrops. It's just a matter "where you draw the line, because a line must exist" $\endgroup$ – Adrian Colomitchi Apr 2 '20 at 5:21
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This brings to mind the personal force shields from Frank Herbert's Dune series. These shields (note that, despite the name, it's a force field encompassing half or all of the wearer's body, not a "strapped to your arm" shield) resist incoming objects with a force proportional to the energy of the incoming object. A bullet, or even a quick blade thrust, is stopped cold, but the shield does nothing to against a slow-moving weapon, so you can still be crushed or impaled, as long as it is done very slowly.

In the case of your mage's robes, rain is not repelled because its approach is sufficiently low-energy that it isn't affected by the parrying enchantment.

On the acid rain sub-question, that's a matter of the material of the robe, which may or may not be susceptible to damage by a particular type or strength of acid, and the sophistication of the enchantment. If the enchantment is "smart" enough to detect threats based on factors other than force of impact, then it may be able to detect and repel the acid. If not, and it responds solely based on threat of impact damage, then acid rain would get through with no problem.

Although, really, if you're dealing with acid rain which is potent enough to damage the robe within the duration of a single battle, I would be far more concerned with what that acid's effects on the person wearing the robe.

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Well, I once wore a bullet-proof vest and it was raining. The vest got wet. No one shot me, but I'm pretty sure that if they had, it would have protected me. This is because rain is expressly not bullets.

Rain and bullets don't work on the same principles.

However, a bullet-proof vest and mage's robe (as you have it) don't seem to work the same way either.

A bullet proof vest works by absorbing the force and spreading it out.

But in your question you actually say the word "parry."

That is NOT the same principle as a bullet proof vest.

par·ry /ˈperē/
verb
ward off (a weapon or attack) with a countermove.

Not the same as absorption. Basically, this means the magic pushes back and deflects against the source. That is also not the same as a force field. Magic that parries a blow is not a force field.

Here's why rain would not be repeled: because in situations other than battle, something that parries against ANY force, no matter how weak, would be...not tenable.

Someone brushes up against you in a crowd--your armor parries. It's not good and not practical, and it can also be a drain on the parry. If there's a finite amount of energy it can expel, pushing off everything from a leaf landing on you to rain is stupid. And it will run out.

I see a few exploits here.

A) IT PARRIES EVERYTHING (but it has only so much energy or energy fed by the mage!!!!!! If it does, I am definitely going to be pelting you with so much gravel, and water for as long as I can, anything that touches the whole surface and causes it to react. Let's not even talk about what might happen if you are made to go SWIMMING in it. The water pressure from every side? Could it be viewed as an attack? Would it be 'smart' enough not to? If it didn't, how impossible would it be to swim???

B) THERE'S A FORCE THRESHOLD FOR PARRIES. Rain, acid or not, is not enough to trigger it. So the enemy might be looking into acids that will damage the parries in places in order that their more ballistic attacks get through.

Look not upon option B as a stumbling block, but as an opportunity. How's it going to be when the seemingly untouchable hero (or villain) gets defeated by a clever person with water balloons and arrows. The first person who figures this out and manages to carry it out is a tactical genius.

Anyway, my take on the info given.

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    $\begingroup$ Looks like you also copied the button to hear how "parry" is pronounced. Makes me wonder which site it was taken from. $\endgroup$ – Clockwork Mar 30 '20 at 11:50
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    $\begingroup$ @Clockwork All I did was google parry. It's the same definition everywhere. Normally I reference a quote, but as it was simply a dictionary definition, I did not bother. $\endgroup$ – Erin Thursby Mar 30 '20 at 20:29
  • $\begingroup$ So... it's sort of like the personal shields from Dune and Stargate SG-1? $\endgroup$ – The Daleks Jun 2 '20 at 0:47
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Too many projectiles

Magic is computable. Each spell is like a computer program, and an enchanted object is like a computer.

Unless the enemy attack completely overwhelm the battlemage in term of magic strength, the robe should survive unscathed.

The rain overwhelms the robe's capacity to process ballistic trajectories. A few droplets do get deflected, but the majority passes through.

By the way, the battlemage should avoid a gunfight in the rain at all costs. A bullet could make it past the robe in that situation.

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Protection of this sort needs to have a lower limit: if it didn't, air itself would be sealed away, and the mage would suffocate in his own protective magic. Given that such a lower limit must exist, a robe tuned so that bullets are stopped would still allow rain through: raindrops hitting the magic would (at worst) atomize into a fine mist that passes through, soaking the mage regardless.

Acid rain in the conventional (pollutant) sense isn't generally strong enough to damage skin or clothing, except perhaps in the long term, and I assume that even magic robes eventually wear out and need to be replaced. For a more concentrated acid attack, I imagine a mage could order the robe to drop that lower limit, sealing off even air and particles (like a hazmat suit). He'd have a few minutes of breathable air trapped inside the protective bubble, enough for him to escape to more congenial surroundings before raising that lower limit again.

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Frame challenge: What if instead of blocking bullets, the robe magically caused the wizard to dodge them? I.e.: it gives him superior predictive capabilities to know exactly where every bullet and arrow is going to be and aids his reflexes (or just physically pushes him out of the way - think of Doctor Strange's robe. Sure this might interfere or distract from his spell casting, but it's better than being shot.) so the shots just miss constantly. Theoretically he could dodge raindrops as well, but this would be a waste of effort and might make it extremely distracting to the point of impossibility of channeling spells in the rain.

(Note that unlike the blocking robes, this would mean there's no protection for other people standing behind the wizard. Those dodged shots might still hit something else.)

This could possibly be defeated by firing a dense enough volley of projectiles that there's simply nowhere he could dodge to and avoid every shot, but this would require a lot of coordination among the multiple archers/marksmen attacking him. Something like a shotgun might have a better chance of doing some damage, but depending on your tech level, these might not be invented yet.

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The enchantment on the robe makes the fibers of the robe invulnerable. In order for an arrow or crossbow bolt to pierce the mage, it would have to sever strands of the fibers that make up the cloth the robe is made of. The magical enchantment on the robe makes that impossible. If the cloth is sufficiently thick enough, or has padding, it will absorb the impact of the projectile without doing much harm to the mage wearing it. It will still hurt, and probably leave a bruise, but he won't get impaled.

But it otherwise behaves like a regular robe. The material is still porous and will soak up water (or any liquid) like normal cloth would. The mage wearing them will still get wet. Acid won't dissolve the robe, but it will dissolve the mage inside, so he still needs to be careful!

The mage would do well to make sure the robes are fitted well before the enchantment is applied. Once the robe is enchanted, no tailor will be able to make alterations!

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  • $\begingroup$ @Matthew, yes, but they won't stop the acid from soaking through. As I said, acid won't dissolve the robe, but the robe won't stop the acid from soaking through and dissolving the mage inside. $\endgroup$ – Seth R Mar 30 '20 at 15:11
  • $\begingroup$ D'oh. I misread that "the magic inside", i.e. the magic that powers the robe's defense. $\endgroup$ – Matthew Mar 30 '20 at 15:13
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Costs

If the enchantment requires a moderate cost to activate or run, then it might be worth activating when the battlemage's life is on the line but not to prevent the battlemage from getting wet.

Alternatively, the enhantment might have a finite active duration (1 hour of invincibility before it loses it's potency) or unwanted side effects (radioactive armor is safe to wear for a battle, but you wouldn't want to sleep in it)

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  • $\begingroup$ This idea works well with the concept of "chip-damage" too, where the robe only gets slightly wet, but over a long time. e.g. "blocks 99.999% of danger!" $\endgroup$ – bobsburner Mar 31 '20 at 10:33
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Your cloak selectively blocks targets according to speed and size.

A raindrop usually won't reach speeds greater than 10 meters per second, while the slowest bullet will travel at speeds superior to 300 meters per second. Even arrows from bows or crossbows can top at higher speeds. That means the cloak selects what it will parry and what it will avoid based on how big it is and the speed it's going at, after all, a slow moving Boulder can be more damaging than a fast needle. Through that mechanism, the wizard's cloak can protect him efficiently while also conserving magic power from projectiles that might actually bring harm to its master.

By this logic, unless the cloak is also capable of analyzing the composition of the incoming projectiles, it might Ignore things like a magic sack filled with acid approaching at sufficiently low speeds, leaving the mage vulnerable to chemical attacks.

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While the raindrop could be counted as a projectile, the resulting puddle/drop of water doesn't. So it can just soak in.

The other thing to consider is how the armour works. Does it have a force requirement, or is it like the armour in stargate atlantis where nothing except air can pass through, or is it more intelligent and works off the users perception? The first and last would be unlikely to stop normal rain, while the last would also stop acid rain. The middle one could kill the wizard, especially if they fall unconscious.

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You can lampshade this concern somewhat cleverly. You still see battlemages getting wet in the rain because the logic of the robes' enchantments isn't completely watertight.

This approach may not be suitable for stories with a serious tone. However for stories with a lighter tone, the use of the word watertight is a double entendre.

Watertight has two common meanings, reproduced below from dictionary.com:

  1. constructed or fitted so tightly as to be impervious to water
  2. so devised or planned as to be impossible to defeat, evade, or nullify

So in one sense, saying the enchantments aren't watertight literally explains that there is a corner case which the enchantment designers didn't account for, which lets rain wet the robes. In the other sense, saying the enchantments aren't watertight lampshades the inconsistency by pointing out that the robes let through rain, usually made of water, and indicates readers shouldn't think too hard about it.

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    $\begingroup$ The OP appears to be asking for a logical reason, not handwavium. $\endgroup$ – The Daleks Mar 30 '20 at 14:20
  • $\begingroup$ @MarvintheParanoidAndroid it's magic thing that stop bullets logic left the station a while ago $\endgroup$ – eps Mar 30 '20 at 16:48
  • $\begingroup$ @eps Worldbuilding.SE assumes that magic follows logical rules; as a result, "handwavium" answers are discouraged. $\endgroup$ – The Daleks Mar 30 '20 at 17:28
  • $\begingroup$ @MarvintheParanoidAndroid The thing is, my answer does give a logical reason, just not in detail. There's some corner case in the enchantments that the designers didn't anticipate which lets rain through. $\endgroup$ – Vaelus Mar 30 '20 at 17:35
  • $\begingroup$ @Vaelus Sorry, the way that you wrote it made it appear that you were advocating handwaving. Perhaps can you add some clarifying detail? $\endgroup$ – The Daleks Mar 30 '20 at 17:38
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Since the robes are protected by a spell, the spell has to have some manner of parameters when it is cast. Parameters combined with intent and power will determine what the spell barrier blocks

I will not necessarily go into how the spell works on a physical level, just how the spell works on a metaphysical level.

The common thread for the battlemage barrier is that it blocks ballistic projectiles. But there are assorted ways to do that, each with their own advantages and drawbacks.

Ballistic projectiles will be negated is one possible way to start with. The intent of the spell is likely to stop arrows, magic, and possibly shrapnel thrown up from near misses from harming the battlemage. Air and the weather are not taken into account with this intent, so its entrance is not negated. As such, the battlemage will still get wet as the rain will not be negated.

Likewise, acid rain will still work so long as it is not magical. Natural acidic rain will still work because it was not considered.

The threads of my robes cannot be broken is another possibility. Since the threads cannot be broken, arrows cannot obviously pierce it nor can magic break them in other ways. This may or may not deal with the forces behind the projectiles unless the intent of the declaration is for the threads to require an arbitrarily high amount of force to break them. Substitute whatever is being worn for robes where necessary.

Again, the rain does not break the battlemage's clothes. If they are made of cloth, then there are tiny gaps between the threads that the water can get into. The threads may also be still able to absorb water in the rain as that is not spelled against. So again, the battlemage can get wet. Acid rain cannot break the clothes, though if it can get into the clothes, the mage itself might not be so safe.

There are other short sentences that can define what your force field spell that your battlemages cast and how they do their thing. Based on the premise that the spell will be based on determine how it reacts to both what it is supposed to and what else might be around.

This also, to some degree, depends on the other rules of magic that you have established (which is not in the question).

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Because parrying a liquid doesn't help.

spell to parry all ballistic projectiles

I would imagine that the spell applies an equal and opposite force to any projectile. When you apply a force back at a bullet (which is solid) it will stop the velocity along with damaging the bullet such as crushing it. At worst you'll end up with bullet dust on your shoulders (anything larger would likely fall off).

However applying a force back at a liquid projectile will cause it to splash (imagine a water balloon breaking) and not entirely stop it (less effective than hitting a solid object). The resulting smaller water droplets should have lower velocity but are equally wet. These smaller droplets are still moving so this process repeats until they are either too small for the spell to track or are moving slow enough that the spell won't apply a parry force back. Either way the water will eventually soak in.

This spell would protect against melee as well as projectiles but must have some kind of minimum size/speed threshold in order for the robe getting wet to be possible (otherwise the water would sit on top of the robe like a rain jacket). This also means that the robe's spell can't be used as a gas mask because gas is smaller and slower than liquid would be.

Real life acid rain isn't acidic enough to dissolve cloth from 1 exposure. It takes many instances over a long time to damage statues etc. But stronger acid would indeed dissolve the robe (and the wearer).

Because the robe doesn't cover the entire body

When you say "robe" I don't think of a dry suit. Presumably the wearer's head, hands, and maybe feet are unprotected. The unprotected parts can easily get wet. Have you ever been wearing a coat and gotten snow down your back? Then you know that an unprotected head means water can get in and soak any part of your body.

see battlemages getting wet

It is entirely possible for a battlemage to be soaked yet the robe remain dry from the spell (as long as the spell also works from the inside out). Given this interpretation the spell has no need for a lower threshold. Even if the spell repels every single atom (including air) the wearer would still be able to breath (assuming he has no face mask with the same spell).

Unless the enemy attack completely overwhelms the battlemage in terms of magic strength

I read that to be a maximum threshold. The spell can only deliver a maximum amount of force and any projectile with more momentum will not be completely stopped. Or perhaps "overwhelming in terms of magic strength" is talking about an enchanted missile (for which rain is not) with an overwhelming amount of magic. The projectile could have a spell that prevents losing momentum in which case whichever spell is stronger would win. For an overwhelming number of projectiles see Renan's excellent answer.

I believe every option I've given for "the spell applies force" meets all requirements of the description.

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  • $\begingroup$ Amendment: I was thinking of a robe without a hood. If a hood is used then the robe shouldn't be water proof if you want to make sure they get wet. $\endgroup$ – SkySpiral7 Apr 11 '20 at 21:38
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The wizard's robes work on the same principle as the force fields from Dune

In Dune it is said that one of the key things that triggers personal force fields is kinetic energy moving beyond a particular threshold. This is why everyone in Dune fights melee battles using swords despite being in the far futures where more advanced firearms like laser guns are a thing, a bullet/laser beam travels at several hundred miles per hour/the speed of light, whereas a sword travels relatively slowly. A raindrop only travels at a speed of about 9 m/s (20 mph), much slower than most ballistic projectiles. An arrow travels at a speed of 67 m/s (150 mph), much faster than a raindrop. By the standards of your wizard robes, an raindrop is not even a projectile worth worrying about.

The weird irony is, though, that in hurricane force winds your wizard robe will likely remain dry, while in a normal downpour it would get soaked.

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