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


Lecture 11.  Machine?


René Descartes (1596-1650) abandoned his plans to publish World and Treatise on Man in 1633, after learning of Galileo's condemnation, but he did not give up his ambition to loosen Aristotle's stranglehold on philosophy by laying a new authoritative foundation based only on clear and distinct ideas. 

The Mechanics of Sensory Perception

He excerpted non-controversial portions of World -- those in which he explained light's reflective and refractive behavior -- and incorporated them in new essays on optics and meteorology.  In 1637, he published these two essays along with one on geometry in a larger work titled Discourse on the Method of rightly conducting one's reason and seeking the truth in the sciences.... 

Meanwhile, in addition to writing and publishing more on his proposed method for practicing the New Philosophy [Meditations on First Philosophy (1641) and Principles of Philosophy (1644)], Descartes continued his anatomical studies, writing down his reflections on the mechanics of human physiology and embryonic development. 

In 1645, one of Descartes' notable correspondents, Princess Elizabeth of Bohemia (1618-1680), pressed him to explicate the nature of the soul and its role in animating the body -- the very topic he had discussed at length in Treatise on Man.  In response to her query, Descartes produced a new essay -- The Passions of the Soul -- built upon Treatise on Man's fundamental physiological principles.  Then, in 1647, he began -- but never finished -- a more complete revision of Treatise on Man simply titled, Description of the Human Body.  He circulated The Passions of the Soul privately until it was published in 1649.  Description of the Human Body was published in 1664 together with the original text of Treatise on Man.

excerpt from
Descartes' Treatise on Man (c. 1632-1640)

[Part 5:  On the structure of the brain of this machine, and how the spirits are distributed there so as to cause its movements and its sensations]

...I desire that you consider that all the functions that I have attributed to this machine, such as the digestion of food, the beating of the heart and the arteries, the nourishment and growth of the bodily parts, respiration, waking and sleeping; the reception of light, sounds odours, smells, heat, and other such qualities by the external sense organs; the impression of the ideas of them in the organ of common sense and the imagination, the retention or imprint of these ideas in the memory; the internal movements of the appetites and the passions; and finally the external movements of all the bodily parts that so aptly follow both the actions of objects presented to the senses, and the passions and impressions that are encountered in memory:  and in this they imitate as perfectly as is possible the movements of real men.  I desire, I say, that you should consider that these functions follow in this machine simply from the disposition of the organs as wholly naturally as the movements of a clock or other automaton follow from the disposition of its counterweights and wheels.  To explain these functions, then, it is not necessary to conceive of any vegetative or sensitive soul, or any other principle of movement or life, other than its blood and its spirits which are agitated by the heat of the fire that burns continuously in its heart, and which is of the same nature as those fires that occur in inanimate bodies.
Descartes' Mechanical Man
Body Part
Mechanical Analogy
heart heat source; causes the expansion of the blood; limited space in the heart forces the expanded fluid out into the arteries; similar to the furnace of a steam engine
valves doors; open and close in response to pressure of blood flow
blood vessels tubes; carry blood to the body's extremities; heavier, less refined blood flows naturally downward and outward from heart; lighter, more refined blood flows naturally upward toward the brain
brain as blood nourishes the brain, subtle animal spirits are produced and stored in the brain's cavities like water in a storage tank
animal spirits fast moving, fine particles that move like a gentle wind
nerves pipes; carry the animal spirit between brain and extremities
pineal gland master controller; monitors and controls the flow of animal spirit
muscles and tendons springs; uncoil and recoil in response to the flow of animal spirit and hence move the bones to which they are attached

The New Philosophy

As the seventeenth century moved into its second half, many thoughtful individuals -- whether they agreed or not with Descartes' method and his mélange of mechanistic notions of how everything from man to universe was structured and operated -- they enthusiastically identified themselves as adherents of the "New Philosophy."

For the New Philosopher, patient observation of natural phenomena no longer sufficed as proof for a claim.  To really get Nature to uncover its secrets, Francis Bacon (1561-1626) had made the case for "tormenting" it by "art."  But not just any experiment would do.  Galileo Galilei (1564-1642) had shown by example that trials must be controlled and involve careful measurement so that the behavior being examined could be described in mathematical terms and objectively compared.  And now René Descartes had reasoned from clear and distinct ideas that even the most complex of natural phenomena could be reduced to a series of simple "mathematizable" mechanical interactions.

A New Role for Instruments

Unfortunately, the natural limits of human sensory perception made it difficult to detect with confidence, and meaningfully compare, the minute differences (in time or weight or length or brightness or color....) found in a set of experimental results.

The idea of extending the senses was not new.  Spectacles were invented sometime between 1285 and the end of the thirteenth century.  Public demand for these optical aids increased between the thirteenth and seventeenth centuries, especially after the invention of moveable type around 1450.  Access to inexpensive printed material by a relatively broad segment of the population revealed a wider range of problems in visual acuity than had previously been suspected.  Spectacle makers responded by producing convex lenses of incremental focusing power to correct varying degrees of hyperopia (far-sightedness) and presbyopia (far-sightedness due to aging), and by developing methods for grinding lenses with concave surfaces for the correction of myopia (near-sightedness).

Improvements made in the optical performance of lenses during this period were, by and large, a haphazard affair.  In the first place, glass of optical quality was a rarity -- something for which lensmakers had to develop a watchful eye.  And, even with the best of available glass, the grinding and polishing of lenses was principally a trial-and-error craft.  By the turn of the seventeenth century, lensmaking remained the province of artisans whose success in producing useful lenses depended on skill and craftsmanship rather than any real understanding of light's refractive behavior.  Scholars of optics showed little or no interest in these matters.

But sometime between 1589 and 1608, a new kind of optical instrument appeared -- a clever device composed of multiple lenses aligned to work together.  One type could make a distant object appear closer enabling details invisible to the naked eye to be discerned.  Another arrangement enlarged images of nearby objects.  Who made these marvelous discoveries? when? where? how? and why?  These are questions to which there are no certain answers.  What we do know is that not long after the introduction of these optical wonders, we find -- for the first time -- individuals with a scholarly interest in the behavior of light becoming interested in applying their knowledge of light's refractive behavior to making practical improvements in the production and use of lenses.

excerpt from
The Preface to Micrographia (1665)
by Robert Hooke (1635-1703)

By the means of Telescopes, there is nothing so far distant but may be represented to our view; and by the help of Microscopes, there is nothing so small as to escape our inquiry; hence there is a new visible World discovered to the understanding. 

By this means [that is, the telescope] the Heavens are open'd, and a vast number of new Stars, and new Motions, and new Productions appear in them, to which all the antient Astronomers were utterly Strangers. 

By this [that is, the microscope] the Earth it self, which lyes so near us, under our feet, shews quite a new thing to us, and in every little particle of its matter, we now behold almost as great a variety of Creatures, as we were able before to reckon up in the whole Universe it self....

[W]e have not yet overcome one World when there are so many others to be discovered, every considerable improvement of Telescopes or Microscopes producing new Worlds and Terra-Incognita's to our view.

Antoni van Leeuwenhoek (1632-1723)

  • born in Delft, Holland
  • educated in local school

van Leeuwenhoek and his microscope

  • apprenticed to a linen-draper
  • returned to Delft; started own business as a fabric merchant
  • friend of artist, Jan Vermeer
  • learned to grind lenses
  • Micrographia by Robert Hooke published
  • traveled to London at which time Micrographia was enjoying great popularity
  • at some time around 1668, possibly before, began making microscopes with single, short-focal-length lenses similar in design to ones described in Micrographia
  • wrote first letter to the Royal Society recounting his microscopical observations of mold, a bee, and a louse
  • submitted report on and illustration of his observations of human sperm

from Philosophical Transactions 12 (1677-1678):  1040-1046

  • sent letter to Royal Society to report on an unusual microscopical discovery in an observation of human sperm; read the text of van Leeuwenhoek's letter for yourself; what can you conclude about his views concerning this observation?
Go to:
  • "The Sand-man" (1817) by Ernst Theodor Amadeus Hoffmann (1776-1822)
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