Let There Be Light! (Optics in Mythic Europe)

While looking at the posibility of using Muto and/or Rego Ignem magic to represent the effects of a parabolic mirror (https://forum.atlas-games.com/t/mechanica-of-heron-can-this-be-done/5388/1), it came to my attention that there are no Muto or Rego guidelines related to light.

Further investigation seems to indicate that Aristotle considered the nature of light to be inherently unknowable and consequently didn't devote much space to the subject in his writings. This explains the lack of Muto and Rego guidelines, but this is rather unsatisfying in Mythic Europe since the properties of light can be studied more directly by the application of magic.

Hence my questions:

  1. What is light in Mythic Europe?
  2. Why is it associated with Ignem rather than Imaginem?
  3. Since Aristotle didn't seem to have an opinion on the matter that we can consider correct in ME, should a modern PoV be substituted or is there another ancient writer whose views should be substituted as authoritative?

Thanks in advance for your replies everyone,

While Aristotle might not have written about light and optics, other medieval philosophers did. I'd prowl Abelard of Bath's "Conversations with his Nephew" and Roger Bacon's works for information.

Matt Ryan

The Authority on Optics is Euclid, in the book of the same title.

this will help

1: light is a facilitator, it only illuminates. Think of film exposure.
2: fire creates light, Imaginem is control of the sensual species. You could use Im to make things look illuminated, but would require changing the species of all things to appear illuminated. Group target.
3:Plato, Euclid, Ptolemy

Isn't there a discussion about light in Ars in the Jerbiton chapter of HoH:Societates?

It's about species, not light as far as I recall. It's certainly about Optics though. I'm not terribly sure what the OP wants though.

In terms of Rego Ignem guidelines, it's true that they do not explicitly refer to light; but it seems that you can freely substiture light for fire at least in the Rego guidelines (see the ReIg spell Light Shaft of the Night from the corebook).

He wants guidelines to manipulate light, not species.


If you go by Arts & Academe, Aristotle is the Authority, not Euclid. Aristotle's theory was one of intromission, not emission as per Euclid. Neither theory does a very good job of describing physical reality, although Aristotle maps pretty well to the IM form of Hermetic Magic. For physics that actually makes sense you need to wait for Ibn al-Haytham (Alhazen to the Medieval West).


That must be a 5th edition change; I wasn't aware. The Book of Optics won't be translated to Latin for a long while. It would change a lot if it were incorporated.

Side note: It makes use of the beginnings of scientific method, which is a bit of an Anachronism especially as it pertains to Bonisagus Original Research, unless you're Persian. Without Arabic or Persian exposure Bonisagus Magi should be coming up with axioms, long logical reasonings, philosophical frameworks, then do an experiment to prove the theory. If the experiment fails the experiment or observation was flawed, change the data not the theory.

Perhaps my choice of wording was less than optimal.... I meant optics in its modern sense as the study of light - not the study of species. Aristotle actually wrote fairly extensively on the latter subject.

Fire creates light yes, but so do the sun, moon and planets all of which exist beyond the lunar sphere where fire, like the other elements, cannot exist. Though the species shed by those heavenly bodies is not only unhindered, but travels to the viewer's eye with tremendous speed. To me all this only adds to the confusion between species and light so I'll simplify my question a bit:

I understand that light stimulates objects to shed visual species and all that is entailed in imaginem. What I'm curious about here is what other properties light possesses in Mythic Europe. Specifically, as per Xavi's example in the linked thread, whether the sun's rays (ignem, not imaginem) can be reflected and concentrated at Touch range in a parabolic reflector to ignite distant ships.

It seems difficult to believe that the ancients failed to notice that the lenses and mirrors they used affected the suns rays as well as "species", but as Jabir noted, Alhazen was the first author to reconcile the Intramission and Emission theories by correctly postulating that the "species" shed by an illuminated object was, in fact, the light itself. This has little bearing on Mythic Europe, however.

Diocles: On burning mirrors ... If you're Arabic or can find some pieces in Greek

Look at Aurum/Aquam Creo and Rego requirements, It looks like its an effect of lower magnitude to use Rego on existing elements. For instance Creo Aquam create water at a high rate of flow is 10 vs Rego of 5. You could have the use of Rego be higher or equal to Creo Ignem as far as creating heat from light, but have a higher Philosophae lead into research for a minor breakthrough that would lower the magnitude of Rego Ignem effects. To simulate a better understanding of the world and incorporating it into magic theory.

Just my viewpoint.

Actually it was apparently translated into Latin around the year 1200. I don't have a better source for this handy than Wikipedia but I know it influenced Roger Bacon a little while later, so I strongly suspect the information is correct. The only reason not to go with Alhazen/Bacon in the game is that real optics don't match up very well at all with IM as presented since 1st edition. It's a bit of a dilemma.

On your side note, I like to think of the proto scientific method as being one of the main contributions of Bonisagus's genius. If Alhazen could come up with this, so could Bonisagus. That's how the OOH got started on its path of semi-scientific incremental development which brought it to the 1220 level of mastery.

I attribute it to Arabic/Greek influence. Alhazen was one of many Arabic and Persian Polymaths that contributed to the Islamic golden age. Aristotle and Plato were criticized heavily by them. Thats moot though since the Hall of Wisdom will be destroyed within a decade of the normal starting time. Which is a bummer.

Experimenting and experience are lesser forms of knowledge for european scholars until the renaissance. But I like the idea of a handful of magical scientists exploring the nature of the universe, in spite of the mundane 'learned' paradigm.

One of the stories attributed to Archimedes is the creation of huge mirrors that did set the roman ships blockading Syracuse on fire. That was the inspiration of the item I wanted to create (before discovering that Mechanica of Heron cannot be used at longer range than voice range...). Just in case you have not figured it, for me Archimedes was clearly a Mechanician :slight_smile:

Do we have any idea where is that story written? Polibius? I am asking because that could be an inspiration for Hermetics to try and do something similar, creating the conditions for the optics debate inside the OoH.


I'm pretty sure that's correct but I'm not 100% sure it was the "Toledo School" of translators in Andalusia or Gerard of Cremona.

There are several popular historical books on this available, including "The House of Wisdom" and "Aladdin's Lamp" etc. Some are better than others.

I looked a lot of this up when I was writing an article on the "Studia Arabum" - a collection of great works written in Arabic (and Persian) that was unknown in the Western world until translated back from Arabic in Iberia in the 13th century. It included a whole lot of Greek works otherwise thought lost - sort of a "Who's Who in Philosophy II" to pad out the Appendix in Art & Academe.

The only thing to come out of this so far is the Index of Books by Ability in the official line (up to HMRE, posted on the Atlas website):

atlas-games.com/pdf_storage/ ... yIndex.pdf

(yes it was a lot of work, no the book rules don't really have the granularity to do medieval science justice but then they're complex enough as it is, yes I am insane to do the index)

I still have the article draft but checking through it, I didn't get to Alhazen but did Alkind, Al Khwarizmi, more Adelard and various others. (Alhazen's pretty cool and I wanted to include him).

Alkindi's (c.801-c.873) contribution would be:
Kitab al-Shu'a'at (Book of the Rays), an Arabic tractatus on optics. Philosophiae (natural philosophy), Quality 10.

I had a thought about several of the books secretly being translated by Hermetic magi in a covenant hidden within the university...



PS BTW, as the Quality of a mundane book is dependent on the author's Com and possession of the Good Teacher Virtue, and independent of the authors actual Ability score (apart from needing a minimum to write on the topic), it's quite easy to create books, especially tractati. Summae are similar, although Level is determined by author Ability score unless you choose to "dumb it down" to make things clearer (improve Quality but reduce Level). Most medieval books are tractati or collections of tractati (and/or encyclopedias) if you read their real world descriptions, particularly as "book" is often used loosely for what we would consider a chapter. If you can guesstimate whether a given author was say better at communicating his message than Averroes but less of a writer than Cicero, you can generate a Quality score easily enough (see table below which won;t come out very well but is in the Excel file).

Alhazen may have more insights than Alkindi but if he couldn't write to save himself, his tractati may be of lower quality regardless of whether he had a Philosophiae (natural philosophy) score of 12+ and a summae written by him may be comprehensive but not necessarily better than reading a whole lot of high Quality tractati, particulalry if you've already got a decent Ability score of 6+. Of course tractati may contain special insights, facts etc that may be of use beyond their value as an XP provider - maybe even the secret of a Minor Virtue that would add some different Guidelines to optic related Imaginem spells etc.

Quality Ranking of Canonical Authors

Examples (from Art & Academe) Quality Comments

(none) 15+
Cicero, Leonardo Fibonacci 14 Com +5, Good Teacher
Hildegard of Bingen, Peter Abelard 13 Com +4, Good Teacher
Aristotle, Donatus 12 Com +3, Good Teacher
Averroes, Avicebron, Gratian 11 Com +2, Good Teacher
St Augustine, Robert Grosseteste 10 Com +1, Good Teacher
Adelard of Bath, Alcuin of York, Avicenna, Boethius, Euclid, Maimonides, Plato, Priscian 9 Com +3 or Good Teacher
St Anselm, Bernard Silvestris, John Scottus Eriugena, Isidore of Seville, Plotinus, Ptolemy 8 Com +2
Macrobius, Rhazes (al-Razi), William of Conches 7 Com +1
Pliny the Elder, Porphyry 6 basic Quality, Com +0
Martianus Capella 5 Com -1
(none) 4 or less Com -2 or below

Note: the Bible is inspirational, rather than educational hence poor Quality but high Level

I do not see why not. That you could make fire by concentrating the sun's heat through a lens was well known throughout antiquity, even to the masses. The following dialogue is not from a philosophical text, but from a comedy (and a really funny one too) of the famous athenian playwriter Aristophanes ("The Clouds", 420BC - about 200 years before Archimedes' mirrors):

Note that this is not about concentrating light, it's about concentrating heat, a different aspect of (the sun's) fire (at least in Mythic Europe) even though a lens actually concentrates both. There's a Rego Ignem spell in the corebook that concentrates starlight and moonlight (Light Shaft of the Night), using the "fire" guidelines, so I fail to see why you couldn't do just the same with heat.

Of course.
It's like the odour of the Sulphur and the toxicity, both are differents aspects of the same objetc (the sulphur).

Wikipedia (for once) actually answers that question :

Very suspiciously, that story only appears century after Archimedes' death, which has fueled controversy ever since. But it was certainly written down, and may well have inspired a member of the OoH to do the same with magic. Although many a Flambeau would argue that Creo Ignem is all you need to set a ship on fire :wink:

Ah yes, thank you!
I'd lost that file somehow.

Do you still have the original file though? Because I think excell may have decided to be your enemy: certain of the books have very curious values in the 'date' column, eg.

Ordo virtutum (Play of Virtues) T 13 music Hildegard of Bingen 22nd century GoTF 130
Symphonia Armoniae Celestium Revelationum T 13 astronomy Hildegard of Bingen 25th century GoTF 133
Symphonia Armoniae Celestium Revelationum T 13 music Hildegard of Bingen 26th century GoTF 134

Thanks, that's a cool index. I'd love to see the rest of your work when you get comfortable with your draft.

That situation is one of the reasons I think tractati should have levels assigned to them. By the RAW an eloquent student can write just as good a tractatus as Averroes or Cicero, despite not having much knowledge of his own. I'd rather say, for example, that Alkindi could produce a Level 8 text and you had to wait for Alhazen to get you a book that would take you towards Level 10.

Yeah, it may very well be a good idea. I was thinking of making tractati level limit that of the writers actual level when writing...
It should make power increases much more manageable and "realistic" i think.