Rhetoric of Science
Spring 2002
Ken Baake
Theories of Light and Their Rhetorical Representations
Based on:
§ Sir Isaac Newton’s Opticks. New York: Dover Publications, 1979, with a preface by I. Bernard Cohen and Introduction by Sir Edmund Whittaker.
§ Oxford Concise Science Dictionary, 3rd ed. Oxford: Oxford UP, 1996.
§ Categories. Aristotle.
§ Gross, Alan. “On the Shoulders of Giants” (from the Harris text).
Light is a qualitative alteration in the medium of air (Gross 24). Aristotle says that reality is made up of substances, which “underlie everything else” (Aristotle 5:15). Presumably, air would be a substance, although I have not yet found his reference to air. These substances can be modified or qualitatively changed. “To sum up, it is a distinctive mark of substance, that, while remaining numerically one and the same, is capable of admitting certain qualities, the modification taking place through a change in the substance itself” (5:15). He sees light holistically, almost more as an ambience than an actual physical entity. Color is an “affective quality” because it affects our perceptions.
Rhetorically, Aristotle develops his argument through a series of definitions, clarifications and logical arguments about how things follow from each other (predicate relationships). The argument is based on reason.
Light is pressure that is transmitted through a plenum
(space filled with particles of matter). The universe is completely full of matter so any
pressure ripples through that matter and, in the case of light, strikes the
eye. The movement occurs as one particle takes the place of the one in front of
it, pushing the latter particle along. Gross
quotes the passage from Descartes’ Discourse on Method where Descartes
develops the analogy of light as a pressure on a vat of grapes that forces
juice out. (Gross 22). So light is pressure lines. Color is caused by the different ways in which matter moves by the force of this
pressure. Different colors result by the different speeds at which the particles
of matter rotate as they respond to the pressure (Newton book, lxv). So color
would be derived from distortions of white light.
Rhetorically, Descartes develops an argument based on reason about how the laws of motion would work. He believes so much in reason (the Classical method of Aristotle) that he claims that if experience is contrary to reason than our senses must be wrong (Gross 25). Still, he acknowledges that not everything can be deduced from reason; we begin to see a role for experiment and a subtle shift in methodology.
Light is a steady
stream of particles (“corpuscles”) that set up disturbances in the “aether” of
space. Newton argues that light is more
than pressure (“pression”)(362-364), but instead is an actual substance of
particles that through the “aether.” This is a membrane like air that vibrates
when struck by the particles. So for Newton, light requires two
substances—particles and the ether membrane that the particles vibrate, whereas
for Descartes light was particles that pushed each other along.
Newton’s early theory and
later theories differed from each other. In his early theory he implied a
duality (particles and waves) in which the corpuscles also conveyed waves that
disturbed the ether (xxxviii). The waves actually caused the particles to
change states, which accounted for color. “Do not several sorts of Rays make Vibrations of several bignesses, which
according to their bignesses excite Sensations of several Colours, much after
the manner that the Vibrations of the Air, according to their several bignesses
excite Sensations of several Sounds?” (345).
So
here we see Newton blending particle and wave theory, which anticipated modern
quantum physics. Color is different wavelengths of light; colors exist first
and only become white light when all of the colors seen together.
But
later in the Opticks he seems to abandon any wave theory, writing “...it
seems probable to me, that God in the beginning, form’d Matter in solid, massy,
hard, impenetrable, moveable Particles...” (400). This may have been in
response to contradictions he saw between the idea of waves and his idea of
mechanical action, offered in his Principia, which postulated that
planets and other celestial bodies moved according to laws of action and
reaction. In the Principia, these forces did not meet resistance from
ether waves (lxxii).
Newton’s rhetorical strategy in the Opticks was sophisticated. His first paper in 1672 failed to persuade because the empirical method seemed radical (Ken Baake’s assumption from the readings) and did not seem reproducible. In the Optics he continued to argue for a new type of thinking. It was based upon observation. It was not based upon the Classical tradition of deduction that moved from premise (hypothesis) to conclusion.
Yet, in the Opticks he softened the impact of his innovative methodology by incorporating many of the Classical argumentation strategies, which would have the effect of showing attention to detail and method, but without alienating readers of the reasoned scientific tradition. The opening of the Opticks reveals this clever strategy: “My Design in this Book is not to explain the Properties of Light by Hypothesis, but to propose and prove them by Reason and Experiments,” Newton wrote, appearing to offer a method that is largely empirical and inductive. Then he immediately sets up definitions and axioms in the finest Classical tradition with this sentence: “In order to which I shall premise the following Definitions and Axioms.” (1). So in a way he is speaking out of both sides of his mouth.
Newton in the body of the book describes in detail his experiments with sentences like this: “I took a black oblong stiff Paper terminated by Parallel Sides, and with a Perpendicular right Line drawn cross from one Side to the other, distinguished it into two equal parts.” (20). He also describes his work with telescope lenses.
Newton, following the new attention to empiricism as argued by Bacon and others, proclaimed that the Opticks would not rely on hypothesis and the deductive method. “For Hypotheses are not to be regarded in experimental Philosophy” (404). Observation, Newton adds, is stronger (more convincing) than logical (Aristotelian) demonstration of conclusions.
Yet, as Cohen wrote in the preface, he certainly allowed his imagination to exceed the evidence (xxii). Gross is correct in writing that Newton’s Opticks reveals an epistemological conflict between the old deductive reasoning method and the new inductive experimental method. The book is full of conclusions about the nature of light and how the ether causes gravity. These conclusions appear innocuous and less assertive, however, because they are framed as negative rhetorical questions (Cohen, Gross). The speculations are the old deductive style hypotheses, but are phrased in a way so as to appear consistent with the new experimental methodology. Cohen writes:
To be sure, the speculation of the Opticks were not hypotheses, at least to the extent that they were framed in questions. Yet, if we use Newton’s own definition, that ‘whatever is not deduced from the phenomena is to be called an hypothesis,’ they are hypothesis indeed. The question form may have been adopted in order to allay criticism, but it does not hide the extent of Newton’s belief. For every one of the Queries [last part of the book, KB] is phrased in the negative! Thus, Newton does not ask in a truly interrogatory way (Query 1): ‘Do Bodies act upon Light at a distance...?’ –as if he did not know the answer. Rather, he puts it: “Do not Bodies act upon Light at a distance...?’ –as if he knew the answer well—‘Why, of course they do!’ (xxxiii).
Hence, Gross argues that Newton did not launch a revolutionary new paradigm in the Kuhnian sense, but instead revised the delivery of his theory in order to satisfy the requirements of both the old methodology (deductive reason) and the new methodology (inductive experiment). Thus, the theory of optics for Gross was evolutionary and not revolutionary (33-35) It is interesting that later theories from Maxwell, Bohr and others of the modern era show light to have both wave and particle qualities. So one could argue that Newton backed away from the true revolution that would come later both in the arguments he made and in the methods in which he made them. Science in this sense is more gradual than Kuhn might claim it to be. Thinking and methods that are ahead of their time will evolve, but not necessarily cause revolution.
We will see this kind of shifting between the old methods and knowledge and the new in Darwin. It is a rhetorical balancing act. Hence, at the Santa Fe Institute we see scientists offering radical new theories and methods (harmonic metaphors) and then retreating to more established traditions, almost denying their radical departure.
Some questions from
class on January 31.
Lacey asked about these physical theories of color: If all the colors together make white light, how would this fit into our understanding of the colors used in paints. When all mixed together they make black. Susan suggested that the difference is that light and paint are quite different substances—the former made up of waves and photons and the latter of oils and pigments. Yes, this is why they blend differently. Lacey’s question was quite insightful, for in fact it is the same question that caused Newton’s contemporaries to reject his early theories of light colors as different states of particles. If this were the case, they wondered, how could the different states of particles mix in paint to form new colors? (lxix). This type of dialogue between Lacey and Susan was certainly knowledge producing and caused me to research Newton more thoroughly.
Pinfan asked a question of me at the end that needed to be asked? Why do we care what the essence of light is? I answered that our understanding of what light is affects the way we use light in applications like telescopes, lasers, etc. I did a little more research to find that indeed the early development of the laser technology in the 1940s was slowed by lack of communication across disciplines about the nature of light. Physicist Charles H. Townes notes in his autobiographical writings:
“I believe whatever unnecessary delay occurred was in part because quantum electronics lies between two fields, physics and electrical engineering. In spite of the closeness of these two fields, the necessary quantum mechanical ideas were generally not known or appreciated by electrical engineers, while physicists who understood well the needed aspects of quantum mechanics were often not adequately acquainted with pertinent ideas of electrical engineering. Furthermore, physicists were somewhat diverted by an emphasis in the world of physics on the photon properties of light rather than on its coherent aspects.” (Townes, Making Waves, Woodbury, NY: AIP, Press, 1995, page 24, italics Ken Baake).
So here we have a prominent scientist arguing that the way in which physicists saw light, both scientifically and perhaps metaphorically, influenced the way in which they were able to conceive of using it technologically. In fact, we know from this history that light was theorized to be either finite discrete particles or a continuum, a kind of substance with attributes (including waves). In fact, it can be perceived as both, which is why it has been so difficult to make sense of from Aristotle’s time to the present.
Thanks to everyone for these great theory-constituting questions.