At the end of Century II of Sylva Sylvarum, Bacon mentions the possibility of making a talking puppet by studying the principles that allow for the production of sound in animate and inanimate bodies:
[S]o that if a man, for curiosity or strangeness sake, would make a puppet or other dead body to pronounce a word, let him consider, on the one part, the motion of the instrument of voice; and on the other part, the like sounds made in inanimate bodies; and what conformity there is that causeth the similitude of sounds; and by that he may minister light to that effect. (SS:199)
Talking heads – of natural or artificial provenience – had been an object of fascination starting with the late Middle Ages and would continue to be one up to the eighteenth century (nineteenth, if we integrate them into the larger tradition of the “learned man’s android” as detailed by Sarah Higley ). Yet the source of their fascination changed dramatically during this period, following a larger trend of naturalizing the preternatural and integrating it into “scientific” explanatory paradigms.
On the natural front, Aristotle had declared severed talking heads an impossibility, on account of the fact that the lungs and windpipe were needed to produce sound (On the Parts of Animals, III:10). Despite this pronouncement, severed talking heads continued their career as a literary and hagiographical motif. Virgil and Ovid depicted the head of Orpheus, still calling out to Eurydice as it floated off to the sea. The heads of Christian saints were sometimes said to keep talking even after they were cut off (St. Edmund the Martyr in Abbo of Fleury’s Passio Santi Eadmundi a good example of this).
On the artificial front, brazen talking heads came to be regarded, in the late Middle Ages, as a symbol of dangerous knowledge. There was little insight into how they were produced, besides the fact that learned men studied the stars for favorable conjunctions to make them. Brazen heads were not to be trusted: legends had them telling the truth in a cryptic manner, so that those who relied on their advice were often led to their death. Among those who were said to have produced or owned a brazen talking head were Virgil (probably because he was a source for the legend of Orpheus), Pope Sylvester II (who was said to have died because he relied on the advice of said instrument), Robert Grosseteste, Albertus Magnus (whose creation was sometimes said to have been destroyed by Thomas Aquinas) and Roger Bacon.
The cover of Greene’s play, showing Friar Bacon’s brazen head
Roger Bacon probably became the most famous of the group, as his example was later used in a popular Elizabethan play of Robert Greene’s, The Honourable History of Friar Bacon and Friar Bungay (~1594). In Greene’s play, the brazen head shatters, after it utters only a cryptic pronouncement (“Time is. Time was. Time is past.”), and Bacon eventually renounces his magic. In this example, as in earlier others, the source of the brazen head’s powers was demonic. But there is something else worth noting in this play, and that is the skepticism displayed by the Oxford doctors towards Bacon’s discovery, which reflects a wider change in attitude during the period. As one of them says:
Have I not pass’d as far in state of schools,
And read of many secrets ? Yet to think
That heads of brass can utter any voice,
Or more, to tell of deep philosophy,
This is a fable Æsop had forgot.
The possibility that someone had ever built a real, autonomous talking head by consulting the stars was challenged by Della Porta, while at the same time an alternative explanation was given: it was possible that the talking head relied on long pipes conveying the sound of someone’s voice from a distance (Natural Magick, XIX:1). The same disparaging of the initial claim, followed by an explanation based on sound being carried through pipes is to be found in Campanella’s Magia e Grazia. (This explanation also happens to nicely parallel an episode from Chapter LVII of Don Quixote, where, steeped as he is in medieval romances, Don Quixote is deceived by a talking head relying not on supernatural powers, but on a system of pipes with a sharp-witted student at the end of them. The man owning the head claims that it was built by “one of the greatest magicians and wizards the world ever saw” who “observed the points of the compass, (…) traced figures, (…) studied the stars, (…) watched favourable moments, and at length brought it to the perfection we shall see to–morrow.”)
While Bacon, like Della Porta, offers a naturalistic basis for building a talking head, his project is far more ambitious, because it deals with imitating and not merely conveying the human voice, by deciphering what makes it possible in the first place.
 Higley S.L.; (1997) The Legend of the Learned Man’s Android. In: Hahn, T. and Lupack A. (eds.), Retelling Tales. Essays in Honor of Russell Peck
 Daston, L., & Park, K. (2001). Wonders and the Order of Nature, 1150-1750.
 Mills, R; (2013) Talking Heads, or, A Tale of Two Clerics. In: Santing, C. and Baert, B. and Traninger, A., (eds.) Disembodied Heads in Medieval and Early Modern Culture