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Bacon- The Founder of the Experimental Method:
Historians of psychology agree that Francis Bacon had the most crucial impact on the development of the experimental method.1 Before him, various groupings of experiments were carried out in the history of science; these include Peter Maricourt's Industria Manuum (it was Peter Peregrinus whom Roger Bacon referred to in Opus Tertium as dominus experimentorum), Thomas Aquinas's Scientia Experientie or its identical twin Scientia Experimentalis, and Nicolas of Cusa's Experimenti Statici. It is common knowledge that not only qualitative but quantitative experiments were already known in ancient times, in medicine, alchemy, and mechanics, among other departments of knowledge.2 Science and scientific methods were valued as the best approach to any area of investigation. This trend culminated in the nineteenth century, when physics was seen as the queen of the sciences, and the more closely a discipline emulated physics, the greater the value placed on that disciplinary inquiry.3
The question of whether science uses a deductive or an inductive method has been around for a long time. The Aristotelian method was deductive, reasoning from the general to the particular. F. Bacon in his Novum Organum of 1620 sought to substitute induction.4 He held that the method of science must be predominantly inductive, proceeding from the particular to the general. Moreover, he qualified his position by building in several critical elements for scientific inquiry. According to him the scientist must be skeptical and not accept formulations that cannot be tested through observation. Rather, the scientist must take a critical view of the world and proceed carefully with the study of observables. Bacon presented a strong statement of empiricism as the basis of science.5
According to F. Bacon, science should include no theories, no hypotheses, no mathematics, and no deduction, but should stay close to the fact of observation. He felt that anyone doing research with preconceived notions would tend to see nature in light of those preconceptions. F. Bacon trusted only the direct observation and recording of nature. With his radical empiricism, he made it clear that the ultimate authority in science is empirical observation.6 In Opus Tertium, R. Bacon points out that mathematics "is the first of the sciences, without which the others cannot be known," that "the causes of natural things cannot be given except by means of geometry," and indeed that the Devil himself brought about the condemnation and neglect of mathematicians because without its service theology and philosophy are useless.7
All this seems to show that Francis Bacon explained induction, skepticism, quantification, and observation, while Roger Bacon explained the application of mathematics to optics; and all these led to the foundation of the experimental method. In fact, it was not R. Bacon or F. Bacon who pioneered these aspects of the scientific method but Ibn al-Haytham. R. Bacon was only a commentator on Ibn al-Haytham's writings on optics. Between the thirteenth and the seventeenth centuries, European books on vision were based on the Latin translation of Ibn al-Haytham's (known in Latin as Alhazen) Book of Optics. For instance, the writings on vision by R. Bacon (1210-1292) are largely commentaries on his writings. The same can be said of other European scholars such as Vittelo (1230-1270) and John Peckham (1240-1291), Archbishop of Canterbury.8
Roger Bacon did achieve considerable success in geometrizing optics. Faced with a variety of opinions on the applicability of mathematics to optics, he followed Ibn al-Haytham in giving mathematics maximum play - even while recognizing that there were problems beyond its reach.9 Ibn al-Haytham's Perspectiva was R. Bacon's guide in his writings, which to a large extent constitute a commentary on Ibn al-Haytham's book. Bacon adopted the idea that only normally incident rays are effective, and he also accepted Ibn al-Haytham's psychological doctrine.10 According to Bacon, that which is coming from the eyes does not mingle with that which comes from visible objects, because what comes from the eye is derived from an animated body and thus differs from what comes from an inanimate object. In this respect there is a regression in comparison with Ibn al-Haytham's theory.11
Boring was wrong; it was Ibn al-Haytham in the eleventh century not F. Bacon in the seventeenth century, who first introduced the notion that science must be inductive. Ibn al-Haytham wrote in Maqala (Book) I of The Book of Optics (Kitab al-Manazir):
It follows from what we have stated and gathered by induction regarding distances that the distances from which an object can be perceived and those at which an object becomes invisible are according to the conditions and properties of the object itself, and also according to the strength or weakness of the sight itself that perceives it. Therefore, from all that we have stated and found by induction and experiment to be uniform and subject to no variation or contradiction, it is evident that sight does not perceive any object that exists with it in the same air and it is not perceived by reflection, unless that object combines the conditions we have stated, namely, that there exists between it and the eye a certain distance proportionate to that object; that it lies opposite the eye.12
A number of scientists agree that Ibn al-Haytham used mathematics and experimental observations in the arena of optics before any one else.13 Throughout Book Iof The Book of Optics,14 he accurately employes the terms experiment, examination, examiner, observer, and find in his study of optics and visual perceptions. For example, he writes: "An accurate experimental examination of this fact" (p. 7); "When the instrument has been perfectly prepared and the experimenter wished to examine the perception of visible objects by sight" (p. 7); "Now when the observer looks at the visible object through the opening in the tube while the ruler lies between the eye and the object" (p. 8).
Sabra15 argues that in The Book of Optics there appears for the first time a distinct concept of experiment consistently associated with three cognate words, i'tabara, i'tibar, and mu'tabir, which the Latin translation of the book rendered as experimentare, experimentatio, and experimentator, respectively. Sabra argued that the appearance of this concept of experiment, being essentially different from the Aristotelian and medical emeiria (almost always expressed in the Arabic literature by tajriba, experience), should be regarded not as a development within Aristotelianism or Galenism but as a "result of taking over into optics an idea [of testing] which had had an established career in astronomy." I'tabara occurs in the Qur'an (59:2) in the sense "to take heed or warning or example from past happenings," the sense frequently encountered in words of history or moral teaching, as, for example, in the title of Ibn Khaldun's famous book, Kitab al-'Ibar.
Thus, in the history of optics, the eleventh century marks a turning point from the classical metaphysical tradition to the beginnings of a coherent experimental and scientific approach. This was achieved by Ibn al-Haytham. His pioneering work in relating the physics of light to the anatomy of the eye created the science of physiological optics.16 The following is the first optical experiment that
he describes in detail in The Book of Optics:
An accurate experimental examination of this fact may be easily made with the help of rulers and tubes. Let the experimenter who wishes to make such an examination proceed as follows. Take a very sound and straight ruler and draw along the middle of its surface a straight line parallel to its sides. Take a hollow cylindrical tube, very straight in length, perfectly round and ending in parallel circles; let its thickness be the same throughout and let it be fairly wide but not wider than the eye socket; draw on its outer surface a straight line extending from a point on the circumference of one base to the opposite point on the other side; and let this tube be a little shorter in length than the ruler. Divide the line along the middle of the ruler into three parts, and let the intermediate part be of the same length as the line on the surface of the tube; the remaining parts on either side may be of any length. Attach the tube to the surface of the ruler, placing the line on its exterior upon the intermediate segment of the line in the middle of the ruler's surface; and make sure that the ends of the tube coincide with the points marking off the middle segment. The tube should be so closely and firmly fastened so that it cannot be loosened or displaced.17
Sabra notes that Ibn Al-Haytham in The Book of Optics consistently eschews the term tajriba, the term corresponding to empeiria in the philosophical and medical literature with which he must have been thoroughly familiar, having himself made at one time summaries of many of Aristotle's and Galen's writings. (He appears to use tajriba in place of i'tibar at least once, in On the Quality of Shadows). According to Sabra, the experiments in The Book of Optics, or most of them, are essentially different in form from both the repeated experiences of the physicians and the "comparisons" of the astronomers. To operate explicitly with such a distinct concept of experimental proof while regularly attaching it to a definite set of terms (i'tibar and its cognate), and thus dissociating it from the idea of accumulated experience or empeiria, was a significant conceptual development in the history of experimental science.18
Ibn al-Haytham's Optics is a consistently mathematical and painstakingly empirical investigation of both light and vision. The hallmark of his unique style is his ability to resolve complex issues into closely interrelated series of experimental questions. Each specific problem is then subjected to a quantitative analysis of its variables under stringently controlled conditions. His series of experiments on the rectilinear propagation of light is a perfect illustration of his method. He uses a dark chamber with a small aperture in one wall to provide a point source of light. Filling the room with dust allows the beam of light to be both visualized and tested for linearity. Changing the atmosphere in the room (i.e., smoke instead of dust), gives the same result. Further checks are made using an inference procedure to disrupt the light beam. By this means he is able to show that light can only travel rectilinearly because the spot of light is only disrupted within a linear path; inference within curvilinear paths is ineffective. This use of the method of controlled observations is probably the first example of modern experimental design.19
His experiments with projected light images are of great importance for his hypotheses about vision and the eye. They provide us with what is, perhaps, the earliest version of the modern concept of conjugate points. In his implicit comparison of the eye with a pinhole camera, Ibn al-Haytham gives us the first modern synthesis of anatomy and optics. His conception of the eye as an optical system is best illustrated by his description of the lens and the optical axis of the eye.20 To operate consciously and systematically with a concept of experiment as a distinct method of proof, and not merely to perform or refer to experiments, was no doubt a significant landmark in the history of experimental science.21 Thus, during the eleventh century he associated psychology with physics or t\abi'a and relied purely on scientific observation as a method of investigation. In this respect he was the real founder of the i'tibar or the experimental method in the history of science in general. This fact contradicts what most historians of psychology have written, giving the major credit to F. Bacon.
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