The question of the microscopic illusion

By the 1960s, another trend appeared that influenced major parts of the later historiography. Bruno Zanobio had begun to show that important preachromatic

microscopists, such as Thomas Willis (1621-1675), John Hunter (1718-1783) and Paolo Mascagni (1755-1816) were “victims of the microscope”, mislead by their instruments, since eighteenth-century microscopes produced a “precise” kind of illusion Zanobio called the reticular-filamentous image. With a special technique and modern

microscopes, Zanobio created anew an analogous kind of reticular-filamentous image similar to the one drawn, in some of their plates, by previous micro-anatomists. The historical point is that the anatomists credited these images with a structural meaning Zanobio had denied any scientific value, because of their modern lack of meaning, and artifactual origin. This experimental-historical study influenced the Italian

historiography of microscopy, by providing it a procedure helping to reconstruct the factors producing illusion. The illusory microscopy, --as it was named among Italian historians-- produced by “bad microscopes”, was thus viewed as a factor adduced to explain the decline of microscopy: “A still incomplete knowledge of optical physics, and defective instruments produced erroneous microscopical observations that could only be corrected much later. And one really understands why, at the end of the eighteenth-century, scientific microscopy could not avoid to expire into a dead-end of which it would only be removed from with the advances on the lenses theory and the improvement of optical instruments”.⁸¹

Considered by Zanobio as a kind of research programme to put into general use for the history of microscopy,⁸² the thesis was actually echoed in many trends, because it eventually supplied historians with “technological proofs” demonstrating that preachromatic microscopes generously yielded artifacts. Luigi Belloni, for instances

81 Zanobio 1961, 593.

82 Zanobio 1971, 38-39.

considered Zanobio’s thesis a leading advance in the history of microscopy.⁸³ The illusory microscopy found many echoes and was applied to the explanation of particular phenomena, such as the globular illusion. Many microscopists, we are told, drew

globular images of animalcules of the infusions and of anatomical sections. Rupert S.

Hall considered globular theories such as Buffon’s, to be the product of the spherical aberration caused by the instrument.⁸⁴ Such a thesis has been developed by Philip Sloan who argued that the microscope Needham lent to Buffon was a Wilson simple

microscope.⁸⁵ Shirley Roe applied as well this logic in considering that for his embryological description of the development of the chicken embryo, “Wolff’s

‘globules’ were most likely optical artifacts”.⁸⁶ The same kind of explanation was recently put forward by Ghesquier about Galès’ determination of the Acarus scabiei in 1816.⁸⁷ In one way or another, eighteenth-century scholars were then almost always regarded as “victims of the microscope”, an expression coined by Zanobio thanks to his anachronistic inquiry.

What does such an investigation mean? There are some methodological criticisms to direct at Zanobio’s work. It is based on five images taken from five books printed between 1680 and 1820, and this should act as a causal explanation accounting for the eighteenth-century failure of microscopy... But Zanobio himself selected his images among hundreds of other images, which do not present the same defect. There is, as well, a flagrant contradiction between the magnification used by Zanobio to obtain his photographic image (x700!) and the average in magnification of eighteenth-century microscopes as was found by Bradbury and Bracegirdle, which is about x50-x60.

Moreover, Zanobio did not imagine other hypothesis to explain the

reticular-filamentous image, such as the possibility that they came from a specific technique used by drawers and engravers to fill up some spaces in a plate. We could perhaps find the

83 Belloni 1961, 1962, 65-68.

84 Hall 1969, 186.

85 Sloan 1992, 424-425. For a reconsideration of that thesis, see Stefani 2000, and chapter 6.

86 Roe 1981, 179. See also Roe 1981, 85-86.

87 Ghesquier 1999, 50.

reticular-filamentous image in an engraving without magnification... How then can one compare an image produced through photo to that engraved on the basis of a drawing, being the normal procedure used for scientific iconography during the eighteenth-century? On top of it, depicting the eighteenth-century scholars as “victims of the microscope” is taking them either for fools or unable to tackle the problem of illusion.

Such an approach neglects two fundamental facts which are the use of the microscope and the scholar’s reactions to the condition of vision yielded by instruments. Are there evidences showing such kind of relation between the scholar and the microscope, and according to what kind of social, historical, technical or geographical factors? It is also likely, through the use of the microscope, that changes emerged during the century, and techniques gently improved. Some research have recently proved that scholars were not passive before the question of the illusion, an issue addressed in the 1750s by a

populariser of the microscope like Henry Baker (1698-1774).⁸⁸

One of the specific concepts put forward to understand more analytically the

functioning of preachromatic microscopy has been proposed by Luigi Belloni --a leader historian of microscopy for half century after second world war. The concept of

“microscope of nature” refers to the ability to select, through microscopical inquiry, an organism which turns paradigmatic to some features to be observed and acquire a more universal meaning. Belloni states that the frog was indeed a good experimental animal through which Malpighi could, with a modest magnification, discover the reticulate net.⁸⁹ Such a discovery would have been much more difficult if undertaken on the human species, for it would have necessitated more powerful lenses. The microscope of nature also explains, for instance, why the instrument makers supplied their customs with the image of a small fish, and perhaps with a true one, in which the circulation of blood was visible. On the other hand, such a concept does not account for the normal activity of most eighteenth-century scholars. They worked like explorer of the variety

88 Mazzolini 1997, 217.

89 Belloni 1979, 143; Belloni 1971, 103.

of the new world of microscopy, which no grand discovery would stem from. But if an organism presents some specific properties that might be selected for observation --obviously one would not study parthenogenesis in cows-- nevertheless, acceptance of a discovery by a community of scholars calls for other kind of procedures. I speak here of the tension between the relative lack of the microscope’s standardisation and the

necessity for the communities of scholars to reproduce experiments and observations in order to record valid knowledge. Since Shapin and Schaffer’s work, the multiplication of witnesses has been considered an important characteristic of a community of scholars for validating knowledge through three technologies: instrumental, social and

rhetorical.⁹⁰ All but eighteenth-century microscopy was considered from this angle.⁹¹ But there are also constraints related to the object and conceptual necessities where the social reproduction of knowledge was forced to deal with cognitive considerations.

Pursuing further this argument, in the next chapters I will show that the use of the microscope, though still controversial --which is inescapable, but so is science-- was mainly in accordance with the reproduction of observation, perhaps the major epistemological dimension required by scientific activity during the age of Enlightenment. The growing adequacy between the possibilities opened by the

instrument and the rules of the communication of knowledge through the reproduction of observations and experiments caused the microscopist to adapt his instrument to organisms that everyone could still afford to observe. Commonly interpreted as the foundation of the experimental biology,⁹² Trembley’s polyp is perhaps more significant when considered the prototype of such novelty in the history of scientific

communication, and I shall investigate the terms by which the polyp became a paradigmatic microscopical object. Indeed, with respect to the practices of the microscope, one of the major stakes of the polyp --so the green fly-- was that it

90 See S&S 1985, 25-26, 55-65, Shapin 1984.

91 See Wilson 1995, 98-100, Harwood 1989.

92 Lenhoff and Lenhoff 1986, 16; Schiller 1974, 185; Baker 1952. Every remarkable scientist was considered an original “founder” of biology, Spallanzani (Rostand 1951, 258-259); Buffon (Binet &

Roger 1977, 165-167) and Lamarck (Pichot 1990, 588).

provided academics with a kind of gauge for a valid standardisation of instruments used to tackle the less-visible and microscopic objects. With the polyp, for the first time, the limits of visibility changed not only for a couple of scholars, but on an European scale.

With such a new object, and with the renewal of spontaneous generation that followed, the 1740s was not only characterised by changes in scientific issues, but also by a rupture in the forms of communication, which, from the standpoint of research with the microscope, allowed for the consummation of a definitive rupture with the past. Part II (chapter 5) will be dedicated to the examination of this issue. Furthermore, a main difference between Trembley and Bonnet’s natural experimental projects with previous projects was that the former were designed as experimental systems and not simply experiments. Appealing for more detailed and accurate reports, enabling the researcher to account for a series of experiments on a series of objects, Trembley also rose the standards of the forms of communication related to such knowledge, as will be shown in chapter 5. The further development of marine zoology and of studies on animalcules from the 1750s onwards shows the efficiency of his heuristic method.

Though the microscope was beforehand a normal tool used in some academic areas mainly to study insects, the debut of the polyp marked the beginning of an irreversible path in looking for more microscopic organisms. Up to the middle of the century, reports on invisible organisms were partly shrugged off from academies for lack of possibilities to share their verification with other scholars. Buffon and Needham’s hints to show microscopic organisms get their meaning partly in relation to such a context. I thus call rationalisation of the practices of the microscope the process by which the microscopists and related networks of scholars tended to adapt the material conditions of vision and the objects of their observations and experiments, as well as their reports, to the imperative of replication. This, for instance, compelled to develop procedures such as the comparison of microscopes, and the uses of many microscopes when observing and experimenting. As well, scholars had to get how to send organisms, and explain their observations, techniques and material used, in order to give colleagues the

opportunity to replicate exactly their own experiments. Rationalisation is also one of the ways scholars by-passed the problem of “illusion”, by sharing observation and

controlling it through repetition, using several instruments instead of only one. In such a history, which I believe enables the historian to draw the lines of force in the

development of natural sciences related to social interaction, scholars like

Leeuwenhoek would obviously not appear to be so important. To the elitist way of using the microscope by Leeuwenhoek opposed the democratic microscope of many eighteenth-century authors. Indeed, if the sensitivity to social circumstances was raised by Ruestow to explain Leeuwenhoek’s commitment to microscopy,⁹³ however many historians have underlined his reticence to play the game of enabling other scholar’s repetition of his observations, of sharing instruments or showing the way to make them.⁹⁴ The relative lack of heirs to Leeuwenhoek’s work thus appears partly as a consequence of his attitude, and in such a respect, as we shall see, eighteenth-century continental scholars always faced the problem of the empirical repetition, regarded as an act with a scientific and social meaning.

My aim here is clearly not to measure the distance between an idealised rationalisation and the results obtained by scholars, for instance in the debate of spontaneous

generation. I do not strive at all for a classification of good and bad microscopists, especially when such a classification is loaded by the results obtained with the classical gauge of their belief in or rejection of spontaneous generation. Much more, the

rationalisation of the microscopical practices stems from the sources and encompasses debates and quarrels as an integral part of its dynamics. In such a process, the analysis of the scholar’s behavior towards new trends and new discoveries appears much more fundamental than the reality of the illusion --though illusion can not be neglected-- produced by the microscopes.

93 Ruestow (1996, 174-175) invoked Leeuwenhoek’s “self-esteem” and “ego”.

94 See chapters 2, 3.