Department of History
University of California, Irvine
Instructor:    Dr. Barbara J. Becker

Week 2.  Transmission Trouble

Natural Questions (c. 1116)
by Adelard of Bath (c. 1075-1160)
Hermann Gollancz, trans.; cited in A Source Book in Medieval Science,
Edward Grant, ed., (Cambridge, 1974):  pp. 376-80.

ADELARD: When not long ago, while [Henry I of England (1068-1135)] was on the throne [1100-1135], I returned to England after my long period of study abroad, it was very agreeable to meet my friends again....  [A] nephew of mine who was with the others--he was interested rather than expert in natural science--urged me to disclose something new from my Arab studies.  To this, when the rest had agreed, I delivered myself in the tract that follows...
NEPHEW: ...if I were only to listen to you expounding a lot of Saracen theories, and many of them seemed to me to be foolish enough, I would get a little restless ... [so] while you are explaining them, I will oppose you wherever it seems fit.  I am sure you praise them shamelessly and are too keen to point out our ignorance.  So for you it will be the fruit of your labor if you acquit yourself well, while for me, if I oppose you plausibly, it will mean that I have kept my promise.
WHY do plants spring from the earth?
NEPHEW: If you collect dry dust and put it finely sieved in an earthenware or bronze pot, after a while when you see plants springing up, to what else do you attribute this but to the marvelous effect of the wonderful divine will?
ADELARD: I do not detract from God.  Everything that is, is from him and because of him.  But [nature] is not confused and without system and so far as human knowledge has progressed it should be given a hearing.  Only when it fails utterly should there be recourse to God....

Those who are now called authorities reached that position first by exercise of their reason....  Wherefore, if you want to hear anything more from me, give and take reason....

WHAT theory is to be held concerning sight?
ADELARD: Many different views have been expressed about the nature of sight, and it will be perhaps convenient first to set them forth, and then inquire which of them is the most reasonable....
NEPHEW: The theories I have been able to collect in various quarters about sight fall into four different groups. 
  • Some say that the mind, sitting in the brain is its chief seat, and looking forth upon outer things through open windows, viz., the eyes, gets knowledge of the shapes of things, and when it has got knowledge of them, judges them; it being always understood that nothing from the mind passes to the outside, and nothing from the shapes outside makes its way to the mind. 
  • Others, again, maintain that sight takes place through the approach of shapes, saying that the shapes of things give shape to the air that intervenes between themselves and the eyes, and that in this way the materials for judgment pass to the mind. 
  • Very many also assert that something is sent forth by the mind, i.e., visible breath, and that the shapes of the things that are to be seen meet it in mid-air:  having taken shape from these, the breath returns to its seat, and presents the shape to the mind for it to exercise judgment upon. 
  • A fourth party maintains that no shapes of objects approach the eye, but that something which they call "fiery force," and which is produced in the brain by means of concave sinews, passes first through the eyes, and then to the objects to be seen, and by returning to its point of origin brings back to the mind, with the same quickness as it went, the shape impressed upon it as though by a potter....
ADELARD: [T]here is another consideration which, even if we put other objections on one side, is sufficient to upset all the views we have mentioned.  It is this:  we are familiar enough with the sight of our own shapes in a mirror; but this, though its reality is established by everyday life, does not agree with the theories we have recounted.  It will be better, therefore, to deal with the view of which philosophy approves, and dismissing other theories as lacking strength, put our faith in this academic truth. 

This theory is as follows:  In the brain there is generated a certain air of the most subtle nature, and made of fire, and consequently exceedingly light:  this makes its way from the mind along the nerves, whenever it so pleases, and necessity arises, to see things outside.  Hence it is called by physicists "visible spirit":  being a body, it naturally requires a local exit, which exit it finds through the different concave nerves, which the Greeks call "optic," extending from the brain to the eyes:  then traveling to the body to be seen, it makes its way with wondrous speed, and being impressed with the shape of the body, it both receives and retains the impression, and then returning to its original position, it communicates the shape it has received.  Now this spirit is called by philosophers "fiery force," and this force, when it finds a mirror opposite to it, or any other light-giving body, being reflected by it, returns as a result of the reflection to its own face, and still retaining the shape, when it enters, reveals it to the mind.  You are not, however, to suppose that this fiery force found the shape of the face in the mirror; but, being reflected from the surface which is too smooth for it to abide there, received the shape while returning, and having received it, brought it back. 

This then is the divine theory which Plato has adopted, among other things, in his Timaeus.  "There are, in my opinion," says Plato, "two virtues in fire, one consuming and destructive, the other soothing and endowed with harmless light.  With this one, therefore, in virtue of which light bringing in the day unfolds itself, the divine powers are in harmony, for it has been their pleasure that the intimate fire of our bodies, own brother of the fire which is a passing bright, clear, and purged fluid, should flow through the eyes, and issue from them in order that through the eyes, slight, cramped, and affrighted, as it were, by the stouter substance, but yet offering a narrow medium, the more subtle clear fire might flow down through the same medium.  Hence, when the light of day lends itself to the diffusion of sight, then no doubt the two like lights meeting in turn cohere into the appearance of a single body, in which the flashing brightness of the eyes meet, while the intimate brightness of the diffusion as it spreads is reflected by meeting with the image at close quarters.  All this then goes through one and the same experience, and the result of that same experience, when either it touches something else, or is touched by it; moved by this contact, it spreads itself through the whole body, and making its way through that body to the mind and produces the sense which is called 'sight.'"

WHETHER visible breath is a substance or an accident?
NEPHEW: I have now a task to impose both on Plato and on you, and I think it will annoy you both:  for if, as has been previously explained, anything issues from the brain, whether with the physicists we call it visible breath, or--as Plato insists--the fire of our own bodies, it must necessarily be either substance or accident.
ADELARD: It is corporeal substance; for, as the philosopher says, fire is a most subtle substance, composed of the four elements.
HOW can this same breath in so short a time travel to the stars and return from them?
NEPHEW: [T]his fiery breath with a single glance of the eye, so to speak, sees the stars; and we have to admit, that a body in so short a time traverses and returns through as great a density of air as there is between us and the moon and the infinite space that lies between us and the moon, and between the moon and the sun up to the very aplanos itself:  and this is mere madness and quite impossible, since the actual breadth of the whole earth bears no sort of proportion to the infinite diameter of the sky.
ADELARD: That is the sort of difficulty that a man gets into who knows nothing of nature:  do you then pay careful attention and store up in your mind what I am going to say.  Just as of spaces some are wide, some wider, and some widest of all, so of bodies some I hold are swift, others swifter, and others swiftest of all.  This, however, not everyone can understand.  Just as the extent of the sky and its shape as laid down by geometers is barely or not at all clear to the vulgar mind, so to it such a great speed in so short a time cannot be clear, though the eye in such people is swifter than the mind; for they measure, or rather mismeasure, everything according to the fallacious evidence of their senses in terrestrial matters.  They think that the size of the sky exactly coincides with the earth, and that the bulk of the moon and sun and other things, which true reason would show them to exceed in size the earth, are not one whit greater than they seem to their bleary eyes. 

Those, however, who in matters of this sort are more apt to use reason, the incorporeal eye of the mind as their guide, ... see clearly the revolution of the heavens and the unutterably swift movement of the visible breath--and this in both cases, thanks to the use of reason....  [T]his visible breath is more subtly perfected by the wonderful energy of creative virtue than all things compounded of elements.  Just as the traveling forth of mind is the cause of that swift revolution, so the traveling forth of body is the reason of this swift going and returning, and it is not strange that the man who is ignorant of this should also be ignorant of and wonder at its effects....

HOW is it that while the eye is shut, the visible breath is not left outside?
NEPHEW: Just imagine that while the visible breath is touching a star, the eye is shut.  This is bound to happen, frequently, and the breath will then be left outside.
ADELARD: If only you would remember what I said previously, you would not raise this objection.  The breath is very swift, and, as said above, it is established that it is sent by the mind, and through the mind.  It is clear that the eye can be closed only by the mind, by which all voluntary motion is communicated to the body; let the consequence then of this also be clear, that that which sends also receives; and when it wills, shuts the door in such a way as to involve no injury to itself; and so that nothing of its own may remain outside, especially too when the thing itself is of such speed that it immediately receives it back again....
WHYthe breath does not hinder itself in going and returning.
NEPHEW: Assume that this breath, or if you will, fire, makes its way as far as to what is to be seen by it:  is sight effected before it returns or afterwards?
ADELARD: It brings no message until its return.
NEPHEW: If therefore sight takes place immediately after its return, when we look at anything for a long while with fixed gaze and see it, it follows that it has both gone and returned at the same time, if we see the thing continuously and without any interval:  hence both its going and returning will be simultaneous and without division, and therefore it hinders itself while going and returning.
ADELARD: Nay, it is you who hinder yourself, for as a result of your not understanding you make foolish objections....  When we say that it goes and returns so quickly, that when one return is accomplished, another starting takes place without a word, because there is no delay perceptible to any sense, since there is nothing that is manifest to sense, i.e., to the intellect, there is therefore no great need that it should go with the same speed after its return as it returned with after its going.  As, however, this interval is not discernible to sense, the journey wrongly seems continuous.
Go to:
  • the "cave parable"  from The Republic (c. 360 BCE), by Plato (428-348 BCE);
  • De Naturis Rerum [On the Nature of Things] (c. 1190), by Alexander Neckam (1157-1217); and
  • The Letter of Roger Bacon (c.1214-1294) Concerning the Marvelous Power of Art and of Nature and Concerning the Nullity of Magic (c.1248).
Weekly Readings
Lecture Notes