Step 1: Create a magic item capable of boiling water constantly.
Step 2: Create another magic item capable of creating water in large amounts many times a day.
Step 3: Read up on Heron of Alexandria's steam engines, and apply your knowledge.
Step 4: ????????
Step 5: Profit!
Please share your insight on the practical applications of the magical steam engine 
.
If you're going to rely on constant magic you can skip the steam bit and just Rego some constant motion. It's less atmospheric but would save waste energy if it were a Newtonian universe anyway.
No need for large amounts of water created, as long as you can create it ALL the time. Duration diameter should be plenty enough.
Aircraft for one thing are 100% realistic with step 1 and 2 combined. There were even some early aircraft that flew with steam engines, and being able to make them hyperlight by removing the need for both boiler and fuel for it, well wow...
And then you combine it with the early ideas(which by the game era has been around for centuries already) for steam turbines and 
steam jet engines... :mrgreen:
Actually, now that neither water nor fuel reserves is an issue, i wonder if steam rocket engines might not be both very simple and effective...
Im not sure "profit" is the best description though! 
The items needed are really reasonably low level.
CrAq Base 2, +1 Diameter duration +10 levels infinite use to keep filling a container endlessly with water, possibly with a linked trigger at +3 levels. Clearly less than 20.
CrIg Base 5 or 10 depending on if fixing the "melt lead" and "red hot" mixup, +10 levels infinite use, possibly with +1 Touch as range depending on how its set up. Less than 30.
2 specialists cooperating and they can quickly make a few engines of one sort or another.
Lol, im getting Recluce vibes here(their warships more specifically)...
Actually i dont agree. Yes it would be a simpler effect, and just one...
However, i think you seriously underestimate how much power you could get from a steam engine based on an endless supply of water and heat. ReTe or ReHe will need quite a lot of Size modifiers and if you compare the Rego base guidelines for making something move quickly, i expect the base to be used is 10 or 15.
The steam engine can just keep creating water that is constantly flashboiled into highpressure steam, directed into a steam piston engine for basic power, steam turbine for some more, a steam jet engine for serious power and an outright steam rocket for excessive power.
It would frankly be rather EASY to make a small vehicle(as in bicycle sized) with more engine power than a Saturn V rocket. :mrgreen:
AND unlike said rocket, it would never ever run out of fuel!
So then hmmm, lets be modest and say we can get 1M kg thrust for a vehicle 1K kg... Hey, i think we´re going to need some little spell to allow surviving acceleration! 1000g worth of acceleration, darn thats just fun.
Magi on Mars! 
(would only take about 45 minutes to get to Mars at a standard halfway acc/dec) 
Problem is that you would splat against the lunar sphere, but hey. 
I just do not buy that in our setting, but it is 100% kosher by the rules
I'd note that since you don't need fuel, you could easily maintain 1 g acceleration and reach approximately the speed of light in relatively short time, allowing you to travel between the stars.
What's that? The lunar sphere? Never heard of it.
(Yeah, I'm a physicist.)
You do need to increase the Size of the CrIg effect to heat up a substantially-sized amount of water to "red-hot" levels, I think. But this still leaves the item viable. The cost in raw vis is not insubstantial, however - I reckon it's best to actually use two lesser enchanted devices, for, what, about 7 or so pawns? Per engine. Not industrial-production affairs, then - think giant mecha!
Pft "lunar sphere"... Even ingame it can be argued that such doesnt even exist. And i most certainly dont include it as a physical barrier.
No need. You specify the amount of water created based on the maximum amount that can be affected without raising size and with "unlimited uses" the creation of water and heat can be made to happen once per round just as well as once per nanosecond... Ie there is never too much water being affected at any single time.
That was what i meant earlier. No need to make it invested items when the levels are reasonably low.
:mrgreen:
I hadn't really considered the differences in energy produced by the Rego guidelines vs. the Creo Ig guidelines. Conceptually it doesn't make much sense that it's harder to magically create pure kinetic rotational energy by Rego than it is to heat up a working fluid and thermodynamically convert it via a turbine or pistons.
Don't forget though, you actually have to create the pressure vessel and other components of your steam engine. Given medieval materials science that's going to take a lot more magic.
I wouldn't use AM rules if I were going to run a game like this. It's not set up for this sort of physics. You might take a look at a strange supplement from the early days of roleplaying called Authentic Thaumatergy, republished by Steve Jackson at some point. I remember it was full of formulas for converting "magic points" into joules and the like. Completely unplayable but very cool.
:mrgreen:
Actually, i already HAVE that book!
It is indeed totally useless as a game system, but its interesting to use for ideas for other games.
It all depends on how extreme you go about making it. Money is rarely an object for magi, so hiring a top notch smith isnt a problem at all, and thats all you need. Medieval science is easily up to creating the components, especially thanks to the most troublesome bits are the ones being replaced by the magic stuff.
What medieval society is NOT up to is to massproduce these things.
The difference is rarely "can" or "cant" make something, but how long it will take and how much less efficient will it be.
Technically speaking, there´s not really anything stopping a 13th century craftsman to build an AK-47, but coming up with the design and then make the ammunition, oh boy thats a BIG problem. Taking up the full time of maybe 2-3 highly skilled craftsmen to make at most a couple of cartridges per day, not very realistic.
The same and similar applies to many modern items, or at least to most things before early to mid 20th century.
After that came the introduction of precision measurement and production, and thats probably the one area that simply cant be copied by a skilled craftsman. The craftsman could still build many things relying on it, but would have to do it individually for every single item, meaning that even a very simple and basic replacement item might take weeks or months to make and fit.
The industrial revolution didnt really introduce anything that couldnt be built before, but it dropped the cost and time of production for many things radically(which in turn fueled the industrial expansion because people could suddenly buy a lot of things for a fraction of the earlier price, especially clothes).
And really, the best variation may very well be an extremely simplified rocket style engine, as that would remove all needs for any complex components. Adding a simplistic turbine to the end of such a contraption can also keep things quite simple, for the very simple reason that there is no need what so ever for tight fittings, because it doesnt matter if the engine is darned inefficient, because you still have free water and fuel.
With Rego you have to control the motion, but with CrIg and CrAq combined you can just pour out as much power as you want, thanks to the "unlimited number of uses per day" addition to an item.
If you want a bit of limitation you could say that unlimited use tops out at once per round(bad idea overall, but might be a good idea in this case), this would reduce the amount of water that can be handled per time, even if it would still be far superior to a real steam engine; or you could require the CrAq guideline to be used to be one of those that creates a constant supply of water rather than "filling a container" and saying that the CrIg doesnt work so well with water quickly flowing past its point of effect while targeting the water requiring it to target a structural part instead which again lowers efficiency. But unlimited fuel and water(not to mention the need for a boiler!) will still mean huge amounts of power compared to size.
OTOH, there´s also the possibility an item that simply creates steam, CrIg(Aq)... Allowing the magical parts for a steam engine per "turn".
What kind of Artes Liberales would you require before you would allow a player to build a magical steam engine? That is, if you would allow it at all. Obviously, the addition of such an anachronism would change the tone of the saga significantly, but would probably not be too unbalanced. I can certainly imagine a genius and highly eccentric Verditius taking the time to craft the infinite steam engine, confusing his colleagues when he produces such amazing results from such low key effects. I think I have my next character idea now 
Anachronism?
en.wikipedia.org/wiki/Aeolipile
en.wikipedia.org/wiki/History_of ... team_power
The concept was either known or repeatedly reinvented(or quite possibly both).
Do be gentle on your poor SG...
That would be Philosophy (natural) rather than AL, if I read A&A correctly: And yes A&A has got rules that could be used to deal with this
In a game where a specialist can start with a penetration in the 40s within his specialty with ease, it is a challenge to find interesting ways to create a highly competent character. You certainly wouldn't be able to tell by looking at the magi's character sheet that he was capable of creating (Palpatine voice) UNLIMITED POWAH! I would only use it with SG approval, of course. The story must (rightfully so) trump cool ideas which are nonetheless out of place.
In other news, I'd use it to power hammers. After all, a self respecting verditius wants the sounds of hammers in his workshop occasionally. Simply turn on the boiler, clang clang clang. And when you disconnect the hammers, it's still providing the heat for your lab.
By creating a Stirling engine you could possibly limit the spell to simply a single CrIg. Although I am not certain if the physics of the age would work the same using Aristotle.
The real question is whether this works in ArM's physics at all.
After all, Heron's toys only worked because of magic.
When you get to that point, why not just enchant things directly? It's not like you can start an industrial revolution. What might be more useful on a mass scale is teaching mundane applied philosophy en masse, or convincing a hedge wizard to initiate mundanes as per Hedge Magic. Or both!
That'll give you a magical revolution.