Wheat from Chaff – Hime’s ‘gunpowder cipher’

Header picture: Mongols using grenades/bombs in 13thC Japan.

preceding posts:

Wheat from the Chaff – ‘Bacon ciphertext
Wheat from Chaff – Books of Secrets and the ‘Secretum secretorum

The “gunpowder recipe”  in Bacon’s  De secretis ..

The essential reference is:

  • H. W. L. Hime (Col.), “Roger Bacon and Gunpowder,” in Roger Bacon: Commemoration Essays, ed. by A. G. Little (Clarendon Press, Oxford, 1914) pp.321-335.

In 2002, while discussing the range of early cipher methods, Pelling transcribed the passage and explained Hime’s rendering of it:

an anagrammatic cipher [which] supposedly transforms… ” luru vopo vir can utriet” into R. VII PART. V NOV. CORUL. V ET … which is allegedly short for…“recipe VII partes, V novellae coruli, V et..”   …the central part of his [i.e. Bacon’s] recipe for gunpowder.

To include mention of that passage from De Secretis in a more specifically ‘Voynich-‘ context would be to accept that some connection exists between Roger Bacon and the Voynich manuscript, and while some form of connection might exist, none has yet been argued from the primary evidence so the ‘gunpowder’ passage from De secretis should be irrelevant, shouldn’t it?

Reeds realised this,  and apparently  so too  did Robert Steele. Reeds’  Voynich Bibliography  includes none of  Hime’s essays and to the listing for Steele’s article (below), it adds a note:  “..about Bacon ‘gunpowder cipher’,  not VMS“.

  • Robert Steele, “Luru Vopo Vir Can Utriet.” Nature 121 (11 Feb. 1928), pp.208-9. The article’s abstract (which is all I’ve seen) mentions another item (NATURE, Sept. 4, 1926, p. 352).

Unfortunately, these are among the few since 1914 to recognise that distinction, the majority distracted first by Hime’s supposing  the passage in De secretis.. proved Bacon invented gunpowder.

A false connection

Combined with Wilfrid’s (also unproven) assertions that the Voynich text was written by Bacon and is in cipher, the topic of de Secretis’   ‘gunpowder cipher’ is included again and again in Voynich-related articles, books and theories to as late the present (2018), when mention is made of it in Dooley’s book:

  • John F. Dooley, History of Cryptography and Cryptanalysis: Codes, Ciphers, and Their Algorithms. (2018).

Dooley’s chosen sources are curious, but the second plainly implies supposing some link to Beinecke MS 408.

     #Brian Clegg, The First Scientist: A Life of Roger Bacon (2003).

     #Lawrence Goldstone & Nancy Goldstone, The Friar and the Cipher: Roger Bacon and the Unsolved Mystery of the Most Unusual Manuscript in the World (2005).

Essentially a biography which turned into a Voynich-themed historical novel, the Goldstones’ book offers no new insight into the imagery, text or manufacture of Beinecke MS  408. see Review by Kirkusthe final line of which is “Many scrambled historical eggs conceal the Bacon.” and The New York Times comment begins:

“When two Westport authors, Lawrence and Nancy Goldstone, decided to write a history of the 13th-century scientist Roger Bacon, they had no idea the trail would lead them to one of the world’s great mysteries. But when they discovered that the brilliant but reviled man of science might have hidden information in a strangely coded manuscript now at Yale University, that became the theme of their new book … ” NYT (Feb 20, 2005).

Seeing how this particular irrelevancy  survived will shed light on the way that other ideas long doubted, or modified, or weeded out entirely from reputable scholarship are still part of the ‘Voynichworld’ landscape.

It was a hundred and three years ago – and before Wilfrid’s talk to the Physicians of Philadelphia –  that Lynn Thorndike explained why the ‘gunpowder cipher’ is likely to be a late addition to Bacon’s original text Writing in 1915,  just a year after Hime’s essay appeared in print, Thorndike wrote:

Lynn Thorndike

“In the first place, the cipher [as asserted by Hime] is based upon chapters of the “Epistola de secretis operibus naturae et de nullitate magie” not found in the early manuscript of that work and considered doubtful by Charles* in his work on Roger Bacon. Indeed, the opening phrases of two chapters, ” Transactis annis Arabum sexcentis et duobus,” and ” Annis Arabum 630 transactis” suggest their source. Secondly. Roger Bacon openly alludes to gunpowder in 1267 in his ” Opus Tertium ” as already in common use in children’s toy explosives. Therefore Colonel Hime has to date the “De secretis” at 1248, and to hold that Bacon was at that time “driven to employ cryptic methods by fear of the Inquisition” (p. 334), but that by 1267

“circumstances had totally changed in the lapse of years; the composition of gunpowder . . . had been divulged, and the first use made of the deadly mixture was for the amusement of children” (p. 321).

But is there any good reason for dating the “De secretis” in 1248? Much of it sounds like a brief popular compilation from Bacon’s three works of 1267-8 concocted by some one else later; compare, for instance, the first paragraph of the sixth chapter of the “De secretis” with Duhem, “Un fragment inedit de l’Opus Tertium,” pp. 153-4 and Little, “Part of the Opus Tertium,” 50-51. The dedication of the “De secretis” to William, Bishop of Paris, who died in 1249, occurs first in the late edition of 1618 and has not been found by Little in any manuscript. Then the inquisition bug-a-boo is negligible. Has any one ever shown that the inquisition punished a practical invention? … it can not be shown that in the thirteenth century the church persecuted men of science. Rather, popes and prelates were their patrons.”

quoted passage above from:

  • Lynn Thorndike, ‘Bacon and Gunpowder‘, Science, New Series, Vol. 42, No. 1092 (Dec. 3, 1915), pp. 799-800. (p.799).

* ‘Charles…’ is presumably E. Charles, author of Roger Bacon: sa Vie, ses Ouvrages, ses Doctrines (Bordeaux, 1861) to whom Thorndike refers several times, not always approvingly.

For current opinion on authorship and dating for De secretis see:

  • Jeremiah Hackett, (ed.)  Roger Bacon and the Sciences: Commemorative Essays 1996 (Brill)

Thorndike’s protest had little effect and for the next half-century, the idea continued to circulate in European popular histories that the invention of gunpowder should be credited to a thirteenth-century Anglo-Norman friar.  What is notable about these writings is an apparent inability to contemplate Europe’s being in debt to Asian, or even Arabic-speaking peoples. Sarton would be among the few exceptions and yet, despite Sarton’s discussion (in 1931),  Lutz  asserts (in 1936) any Oriental or Arabian origin ‘disproved'(!!). (Cf. header picture and illustration below, right).

Meanwhile, Six years after Thorndike’s first protest,  he had again (1921) objected to the constant repetition of the idea that Bacon invented gunpowder, in a letter to  Scientific American which I’ve already reproduced in part.

No noticeable diminution in the idea’s popularity followed, and then

20 years later (1936) , a paper by Edward Lutz again repeats as if they were facts established that  Roger Bacon wrote the Voynich manuscript, and invented the telescope,  the microscope… and gunpowder.

Friar Bacon and hypothetical telescope. From Lutz (1936)

Of gunpowder, Lutz wrote:

“Invention of Gunpowder: In this connection a few words about the invention of gunpowder seem to be in place. If nothing else, Friar Roger was the first European to make mention of gunpowder.[a]  Since its Chinese and Arabian origin has been disproved, we may add that good arguments exist for its actual invention or chance discovery by Bacon during his long life of research. He wrote about gunpowder’s main characteristics before anyone else [sic!] had even mentioned the substance. He possessed its exact chemical formula and hid it within a subtle cipher.[b]

[a] citing, (as n.244)  – W. W. R. Ball, History of Mathematics (1919), p. 174.  [b] citing  (as n.225)  W. R. Newbold,  Cipher of Roger Bacon, pp. 141-143; and Hime’s article  “Gunpowder” published in the Encyclopaedia Britannia (1929). Vol. 2  p. 890.

  • Edward Lutz, ‘Roger Bacon’s Contribution to Knowledge’, Franciscan Studies, No. 17, June, 1936), pp. ii-v, vii-xi, 1-82.

And , dear reader, if you’re thinking  Lutz  was an outlier  –   think again.

Thirty-five years after Thorndike’s critique, now (in 1950) a young Hochberg attempts to judge the matter without doing more than exercising logic on a prohibitively narrow range of data, and all at the level of secondary opinion. The result is erroneous conclusion.

detail from the ‘Mara Buddha’ –  foreign ‘demons’ attack Dunhuang’s Buddhist enclaves. (10thC AD). One fire-propelling item is understood to be a grenade and the other a fire-lance.

A further controversial question concerning [Roger] Bacon’s achievements is whether or not he discovered gunpowder. … Colonel Hime, in perhaps the most authoritative work on the question of Bacon and his relation to the discovery of gunpowder, concludes that Bacon, in the face of the evidence, must be considered to be the discoverer of gunpowder … While it is true that Hime’s conclusion depends upon a certain amount of hypothesizing and conjecture … the conclusion is far from being unreasonable. Nevertheless, both Thorndike and Sarton have challenged the theory that Bacon discovered gunpowder. Their attack centers on Hime’s proposed decipherment of the De Secretis (15, pp. 688- 691; 12, pp. 957-958, 1037-1038). Sarton, however, seems to admit that the issue is not decisive…

  • from Herbert Hochberg, ‘The Empirical Philosophy of Roger and Francis Bacon’. Philosophy of Science, Vol. 20, No. 4 (Oct., 1953), pp. 313-326.

The aim in referring to Hochberg’s essay from so long ago is not to criticise Professor Hochberg for youthful errors;  but to make clear that an exercise of logic cannot make up for a failure to determine the facts by research –  and further that to rely on no more than a limited sample-range – especially of secondary opinion – is to beg the questions they left unasked.  In this instance, the critical question was  not, as Hochberg supposed (more than half a century ago), “which of these secondary authors’ ideas do I think most plausible?” but ‘Where and when do we find our earliest testimony to the existence of gunpowder?”

 

Sixty-three years later, (in 1978) d’Imperio’s Elegant Enigma – whose subject is the Voynich manuscript – includes three of Hime’s essays in its bibliography,  though d’Imperio herself adopts a non-committal tone in the main text:

A considerable literature exists, dealing with ciphers attributed to Bacon in alchemical works.  An anagram in which Bacon is said to have hidden a formula for gunpowder [in de secretis] is explicated variously by some but debunked by others. [the sources are cited – Elegant Enigma, pp.66-67).

Note that d’Imperio does not ignore, but fails to credit to its source, Thorndike’s opinion that the cipher-passage is a later interpolation to De secretis, and also fails to see that the entire question is irrelevant to study of Beinecke MS 408, given lack of any positive evidence for correspondence between Bacon’s extant works and the Voynich manuscript.

Who did invent gunpowder? 

The question was settled beyond all reasonable doubt by Joseph Needham, whose 700-page study was published fully thirty years ago.

Yet …

One hundred and two years after Thorndike’s protest, and thirty-one years after Needham’s exhaustive study,  when Craig Bauer (rightly) asserts (2017) that Hime’s decipherment of the passage in De secretis remains in dispute – his footnote includes not only Hime’s publications about the passage from De secretis but also that Voynich-themed biography of Roger Bacon later referenced by Dooley!  What uncertainty exists is not, today, where gunpowder was first invented but only about which European friar ( Friar Roger or Friar Berthold) first knew its method for manufacture.   And that dispute has no demonstrable link to the Voynich manuscript, at all.

  • Craig P. Bauer, Unsolved!: The History and Mystery of the World’s Greatest Ciphers from Ancient Egypt to Online Secret Societies (2017), p.23 (and notes p.532).

re: Friar Berthold – the legend persisted to 1911.  See the linked entry which cites

  • Hansjacob, Der Schwarze Berthold, Der Erfinder des Schiespulvers u. der Feuerwaffen (Freiburg, 1891).

 

from Needham, op.cit., (p.51).

[following paragraph added Jan 4th., 2019] Manly had provided a lucid dismissal of the ‘gunpowder cipher’ in 1931, writing:

a) The Gunpowder Formula. The briefest and simplest case of a decipherment obtained from a text not written by Roger Bacon is furnished by the famous ‘Gunpowder Formula’.. Here, in a letter attributed to Bacon, occurs, according to Brewer’s reprint from the printed text of 1542, the famous: ‘Sed tamen sal petrae LURU VOPO VIR CAN UTRIET sulphuris; et sic facies tonitruum et coruscationem, si scias artificium.’ I shall not now insist upon the probability that the last three chapters of this epistle are not the work of Bacon, or upon the fact that without any warrant Professor Newbold took a well-known symbol for Sed as Sume. The important fact is that the letters LURU VOPO VIR CAN UTRIET are not found in any extant MS., but are apparently due to a misreading of the distorted Greek letters occurring at this point in the MS. from which the 1542 edition was printed. Yet applying his system to this misreading, which originated more than three centuries after the death of Bacon, Professor Newbold got a thoroughly satisfactory decipherment.

  • John Matthews Manly, ‘Roger Bacon and the Voynich MS’, Speculum, Vol. 6, No. 3 (Jul., 1931), pp. 345-391.

 

  • an anonymous but informative website on the history of gunpowder is here.

 

How did Bacon come to know something.. anything… of gunpowder,?

In terms of European knowledge, the usual opinion is that he learned it from Friar Berthold, or vice versa.  Not that the question has any demonstrable relevance to study of Beinecke MS 408,  but Needham’s view was that:

… Perhaps the most extraordinary fact is that all the stages, from the incendiary uses of the mixture right through to the metal-barrel hand-gun or bombard, with the projectile fully occluding the bore, were passed  through in China, before Europeans knew of the mixture itself. Probably there  were three comings. Roger Bacon by c.1260 or so was able to study fire-crackers, doubtless [sic] brought west by some of his brother friars; and the Arabian military engineers in the Chinese service must have let Hasan al-Rammah know about bombs and rockets by  c.1280. Then, within the following twenty years, came the cannon, quite possibly directly overland through Russia.

  •      Needham, op.cit., p. xxxi.

 

See also:

  • Lynn Thorndike, ‘The True Roger Bacon’ published in two parts in  The American Historical Review. Part 1 in Vol. 21, No. 2 (Jan., 1916), pp. 237-257; Part 2 in Vol. 21, No. 3 (Apr., 1916), pp. 468-480.
  • the current version of the wiki biography for Roger Bacon is good.(Dec. 2018)

 

Next post: The Military Cryptanalysts (Prelude).

Wheat from the Chaff – ‘Bacon ciphertext’

Header picture: detail from Brit.Lib. Add MS 21917 f.71v

The two posts previous to this are:-

The radiocarbon dating which, in 2011, finally ended efforts to describe the Voynich manuscript as an autograph by Roger Bacon, also saw the perhaps arbitrary abandoning of his view that the appearance of the manuscript, and the content, suggested origin in works from the thirteenth century.  No-one has taken on the task of testing whether the content mightn’t be a fifteenth-century copy of a thirteenth-century text (by Bacon or anyone else) but another problem with Wilfrid’s narrative is the limited range and type of techniques for enciphering that were known in Europe before 1400. Not that we necessarily accept that the written part of the text is in cipher.

I add the above paragraph as clarification today (29th Dec. 2018) because I hear on the grapevine that this blog, whose aim is to demonstrate the need for a re-visiting and revising of ideas long-held or tenaciously maintained about the manuscript,  is  being rumoured an effort to  re-instate  Wilfrid’s ‘Bacon ciphertext ‘ idea. ….  **sigh**

Bacon’s cipher methods

Note (updated 18th. Jan. 2019).  Whether it still applies, or was just a touch of influenza, just before this post originally went up, Nick Pelling  had said that he felt discussion of  methodologies inappropriate for his site.  Time mellows many opinions, of course.

 

Bacon  described seven methods by which a text might be rendered obscure in his  De Epistola de Secretis …  (“Letter concerning the marvellous power of art and of nature and concerning the nullity of magic“).

I’ve transcribed the  section in a separate Page (‘see right: Addendum…’). adding some explanatory notes from  John Dooley’s book[J.D.]  and a couple of my own. [D]

The same Page illustrates and links to Aethicus/Ethicus’ alphabet.

Newbold said in 1921, and Power remarks more recently, that Bacon felt great admiration for Aethicus.

( Wilfrid addressed the Philadelphia College of Physicians on the same occasion that  Prof. Newbold delivered the  Fifth ‘Mary Scott Newbold’ lecture.  Newbold held the chair of Intellectual and Moral Philosophy at the University of Pennsylvania, and speaking dates are planned well in advance, so it seems a reasonable assumption that Wilfrid’s invitation was due to Newbold’s good graces.)

  •  Roger Bacon and ciphers. Addendum to…’
  • John Dooley, History of Cryptography and Cryptanalysis: Codes, Ciphers, and Their Algorithms. (2018)
  • Amanda Power,  Roger Bacon and the Defence of Christendom, ( 2013) pp.221-2.
  • Professor Romaine Newbold, ‘The Roger Bacon Manuscript’, Transactions of the College of Physicians of Philadelphia, Series 3: Vol.43, (1921)  pp. 431- 474. Section occurs pp.456ff.

Illustration: (detail)  Roger Bacon, Wellcome Image V0000284

Some early ciphers

Scholars are yet to pay much attention to European ciphers pre-1400, and the seminal paper is still regularly cited:

  • Bernhard Bischoff, « Ûbersicht ûber die nichtdiplomatischen Geheimschriften des Mittelalters», Mitteilungen des instituts fur Osterreichische Geschichtsforschung 62 (1954) 1-27.

but see also:

  • Katherine Ellison and Susan Kim, ‘Introduction: Ciphers and the Material History of Literacy’, in Ellison and Kim (eds.), A Material History of Medieval and Early Modern Ciphers: Cryptography and the History of Literacy.  (New York: Routledge, 2018).

The best known study of early cipher available in English is surely

  • David A.King, The Cipher of the Monks. (2001) The table of contents is (here). King’s work was introduced to public Voynich discussions online by Nick Pelling in 2010, while discussing a 14thC astrolabe from Picardy. (here).

An English cipher, in de Foxton’s Liber Cosmographiae (composed in Oxford in 1408):

  • John Block Friedman, “The Cipher Alphabet of John de Foxton’s Liber Cosmographiae,” Scriptorium 36 (1982), 219-35. accessible as a pdf through Persee.   I have now also found a note by (the honorable) Marco Ponzi who says (here) that de Foxton’s cipher was introduced to  Voynich studies by  Nick Pelling, in a comment to the first mailing list (in 2002).

 

The history of ciphers is older than Bacon, of course.

The cipher, part of which is shown in the header dates to the late tenth century, from the Abbey of Luxeuil and according to the catalogue entry at the British Library reads:

Hbfc Stfphbnxs scrkpskt p[er] prfcfptb brchkinb[er]tk mbgkctrk’ – solved by Sir Frederic Madden to read:  ‘Haec Stephanus scripsit per precepta Archimberti magistri’ (‘This was written by Stephanus at the command of Master Archimbertus’).

The first reference below describes an ostracon (MMA 14.1.219)  said to date from before the eighth century AD.  I have chosen this example partly for its age,  and partly because the editors describe the cipher as one formed by ‘the mixture of several types of letters’ – which is the fourth method described by Bacon in thirteenth-century England.  That ostracon also lets me send a nod to  Georg Baresch,  who believed the Voynich manuscript contained  ‘ancient’ and ‘Egyptian’ matter  as he made clear when asking Athanasius Kircher’s help to identify  the Voynich script.

  • Paulinus Bellet, ‘Anthologia Palatina 9.538, ‘The Alphabet and the Calligraphic Examination in the Coptic Scriptorium’,  The Bulletin of the American Society of Papyrologists, Vol. 19, No. 1/2 (1982), pp.1-7.
  • cf. Liv Ingeborg Lied, Hugo Lundhaug, Snapshots of Evolving Traditions: Jewish and Christian Manuscript Culture, Textual Fluidity, and New Philology (2017) p.157 & note.
  • Letter of Georgius Barschius to Athanasius Kircher (1639). Transcription, translation and notes by Philip Neal.

Apropos of Baresch’s ‘guess’ that the manuscript’s content relates to medicine:

  • George W. Corner, ‘A Thirteenth-Century Medical Cryptogram’, Bulletin of the Institute of the History of Medicine 4 (1936) 745-750.

Several researchers have commented on similarities between the Voynich script and other scripts, including Coptic. One sometimes sees observations of this sort collected – sometimes with attributions included – at agglomerative sites such as  voynich.nu.

 

Why would Bacon want to write in cipher?

“the Franciscan friar, Roger Bacon, an infinitely greater scholar, who had been persecuted on account of his writings and whose scientific discoveries had been misrepresented as black magic. Moreover, for many years he had been forbidden by his Order to write, and he himself referred in his works to the necessity of hiding his great secrets in cipher.”

As far as I know we have not a  scrap of evidence to show that Roger Bacon ever wrote at length in cipher, and Wilfrid appears not to have known that his conception of Bacon as ‘persecuted scientist’ derived ultimately from the Draper-White thesis, which had been refuted in print four years before Wilfrid laid eyes on his ‘Bacon ciphertext’.

James Walsh had written in 1908,

That Dr. White’s book, contradicted as it is so directly by all serious histories of medicine and of science, should have been read by so many thousands in this country, and should have been taken seriously by educated men, physicians, teachers, and even professors of science … only shows how easily even supposedly educated men may be led to follow their prejudices rather than their mental faculties …

And in 1921, Lynn Thorndike  again objected to that ‘persecuted scientist’ notion when writing to Scientific American (see end of post).

Despite objections from persons both intelligent and well-informed, the myth/’theory’ of Bacon’s persecution ‘for science’ continued to be promoted and thus to infect writings for the rest of the twentieth century.  As example of their tone I list the publications from 1922 ( from Reeds’ Bibliography).

  • Feb 4th., Cons, Louis, ‘Un manuscrit mystérieux: Un traité scientifique du treizième siècle, attribué a Roger Bacon’, L’Illustration 159 (Number 4118, 4 Feb 1922) p. 112. [Copy in BL Facs 439. J.R.]
  • May 20th., Garland, Herbert. ‘A Literary Puzzle Solved?’ Illustrated London News 160, (20 May1922), pp.740-742.
  •  Dr. R. Loeser. “Roger Bacons Chiffremanuskript.” Die Umschau. 26 (1922), pp.115-117.

When Bacon was censured, it was in England, and as a result of his serving as ‘whistleblower’ when requested by the Pope to write about poor management and practice in the church in England. Others claim Bacon incurred displeasure by taking it on himself to criticise the system of education decided by ‘elders and betters’ in the church hierarchy.

Natural History?

Bacon’s contemporary, Thomas of Cantimpré (1201 –1272), wrote at great length about natural history, in his ‘De naturis rerum‘, a text that was (so to speak) ‘an instant run-away best seller’, being soon  translated into French, Belgian and German vernaculars.  Clearly, ‘natural history’ didn’t have to be hidden in cipher during Bacon’s lifetime.

The following illustration, comparing script in a fifteenth-century copy of  Cantimpré’s thirteenth-century text with script taken from one folio of Beinecke MS 408, was first published by the present author in May 2016.   That post was one item in a  more detailed exposition of  the internal evidence which indicates the content’s evolution over time. The last substantial stratum, prior to the present volume’s manufacture,  I have dated to the period between 1250 and 1330 AD, that conclusion confirming an earlier opinion (by the present author) which had been reached and shared in posts online by 2011.  Certain minor alterations, additions and marginal inscriptions were treated separately.

illustration from D.N. O’Donovan, ”An early 15th C copy of a 13th C text: Thomas of Cantimpré’, voynichimagery (blog), May 9th., 2016. I regret that in 2017, after almost a decade of being obliged to protest plagiarism and  other abuses, I withdrew from  public access the research I’d shared online.

Postscript:  I am indebted to correspondent for reference to a comment made by Derek J. de Solla Price in 1975, indicating that some had earlier wondered if this might be the case:

Scholars … have surmised that it may well be a copy of a lost original— a fifteenth-century copy of a thirteenth-century text.

  •  The Metropolitan Museum of Art, The Secular Spirit: Life and Art at the End of the Middle Ages (1975) p.203
  • The interesting work recently done by Koen Gheuens, tracing examples of an anomalous form of  ‘lobster-style’ Cancer, refers to Cantimpré’s work. It is worth readers’ attention, though here will be left for a later series.

Aristotle prohibited?

In theory –  only in theory –  it could be argued that there is a period of about ten years when Bacon might (just ‘might’) have needed to encipher some text attributed to  Aristotle.

As mentioned in the previous post, the Arts Faculty of the University of Paris were told in 1210 that:

 “Neither the books of Aristotle on natural philosophy or their commentaries are to be read at Paris in public or secret, and this we forbid under penalty of excommunication.”

On the other hand, members of the Faculty of Theology could read what they liked, and no prohibition existed at all in England.

Bacon came to Paris while the ban was in place (at least nominally), arriving in 1233/4 and remaining until 1250, according to some accounts.  But the Stanford Encyclopaedia of Philosophy says Bacon was already “teaching Aristotle’s works on natural philosophy and metaphysics by the 1240s”, and a ‘British Heritage’ article says Bacon was invited to Paris in 1241 “to present a lecture series on the Aristotelian corpus.”

Which would leave only the period between 1233-c.1243(?) when it might have been necessary to obscure the content of a notebook or some Aristotelian text.

In Paris again by 1257, Bacon would have now found Aristotle’s works freely available:

By 1255,  all of Aristotle’s works were available plus a range of commentaries and expansions of his ideas. [These] were not only widely read in Paris but were prescribed texts in the Arts Faculty.

 

Next post:   medieval ‘Books of Secrets‘; Aristotle’s Secreta Secretorum; and Roger Bacon’s ‘De Secretis