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Not Theory-laden, not Realistic: Experimental Cognition in Microscopic

Observation in the Seventeenth Century

Jens Loescher, Freie Universität Berlin

“Practice — and I mean in general doing, not looking — creates the ability to distinguish

between visible artifacts of the preparation or the instrument, and the real structure that is seen

with the microscope. This practical ability breeds conviction" (Hacking 1985, 137)

“Shapin describes how Leeuwenhoek borrows the prestige of notables to endorse his

observations; but the more elementary fact is that the uncredentialed, socially difficult

Leeuwenhoek achieved authority because of what he saw”. (Wilson 1995, 171)

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The microscope is the small brother of the telescope. The ‘early’ microscopes were double-

lens, ‘Keplerian’ optical systems. Of course, microscopes up to the beginning of the

nineteenth century produced a multitude of artifacts: mostly due to spherical and chromatic

aberration. The former is caused by the fact that the refraction at the edge of the lens is greater

than in the center. The latter is pointing to the problem of varying degrees of refraction of

light of different colours. This effect is particularly devastating in compound microscopes

where the light is refracted several times and the image of the specimen therefore is

surrounded by color fringes.

One school of microscopic invention, the English, headed towards more complicated

apparatus, especially with Christopher Cock, Neremiah Grew and, of course, our patron

Robert Hooke, who nevertheless grudgingly conceded that though “offensive to his eyes, tis

possible with a single Microscope to make discoveries much better than with a double one,

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because the colors which do much disturb the clear vision in double microscopes is clearly

avoided in the single” (Fournier 1996, 13). Hooke relates to the Dutch current of

simplification of the instrument, a purified version of instrumental magnification, consisting

basically of a single spherical lens.

Illustration 2

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The design of the typical Leeuwenhoek-microscope would be this: a brass block stage of

rectangular cross-section, a specimen pin, a main screw, a single lens. And that is it. Were it

not for the extraordinary quality of the lenses Leeuwenhoek was able to grind (in some of the

nine surviving microscopes modern calibration methods have demonstrated a magnification

up to 120 times of the specimen original) one could speak of spectacles with some additional

equipment.

II

There is a couple of ‘old chest-nuts’ in research on microscopy, as Liba Taub has put it (Taub

1999, 732), one of them being the 'lost eighteenth century'. Indeed passing the 1680s there is

one lonely watch tower of microscopic research: Antoni van Leeuwenhoek who incessantly

sends his missives to the Royal Society. In contrast to the telescope there is no theory for the

epistemic phenomena encountered with the microscope. There is no grasp of cellular

structures, there is no understanding of microorganisms, there is a very limited theory of laval

metamorphosis — still over-formed by ‘spontaneous generation’ —. The preference of

Newtonian atomism, basically: particles following the laws of gravity, of mass, of attraction

and repulsion forms an undercurrent in quite a few observations of Leeuwenhoek. That

'Newtonism' proved utterly dysfunctional for microorganisms. On the whole, theory does not

keep pace with experimental output. Therefore, that is the old chestnut, the experimental

output ceases until the beginning of the nineteenth century.

If this is so, why did microscopic observation flourish in the first place? It is not theory-laden

and it is not realistic in the sense that we simply ‘see through the microscope’, as a famous

Hacking-sentence runs. What, then, enabled the five great microscopists of the seventeenth

century — Leeuwenhoek, Swammerdam, Hooke, Malphigi, Grew — to get started and go on

with their work? It is precisely because there is no 'theory-ladenness' and no ‘reality’.

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Observation and apprehension of the microscopist need to be adjusted ‘from within’ to the

environment of the experimental setting (instrument, specimen, light). It is cognitive practices

which do the job of closing the lacuna between epistemic phenomenon and the ‘faithful eye’.

So, it does not make sense to shy away from an individual brand of cognition in the context of

an ‘experimental history of science’. In fact, there is no way around it. There are three

emergency exits for the historian being trapped in this uncomfortable situation: one is a Neo-

Kantian approach which explicitly deals with the way nature (for instance) is transformed into

transcendental categories via ‘practices of reason’, ethical maxims, and emotions. A

transcendental scientific self is responsible for these operations. The second line of argument

rests on the various versions of distributed cognition, ranging from Ludwik Fleck to Edwin

Hutchins’ 'Cognition in the Wild’. Now it is individuals performing cognitive practices

ending up in the construction of epistemic objects. But these individuals ‘see’ according to

collective schools, mental models or pragmatic frames. Third, in a kind of Sennett-like-

approach a materialistic hyperrealism is put forward: There is a 'dialogue' between the thing to

be worked on and the operating person — sometimes, in the robust version of recently

evolving ‘engineering studies’, the material ‘talks back’ and guides scientific innovation.

Now, what I would like to put forward here, is a brand of experimental cognition. In the

experimental situation the scientist activates certain cognitive practices which help him to

bridge the epistemic gap between thing observed, image seen, and construction of meaning.

These cognitive practices might be collectively ‘learned’, but it is important to realize that

they are activated ad hoc in the experimental situation. Although cognitive practices might be

'fixed' knowledge which has been learned or gained, they are 'processed' (combined, etc)

'from scratch' depending on environment, material, constraints of the experimental situation.

Since there is a historical stratification for ‘ins’ and ‘outs’ cognitive practices need to be

defined for the specific historical level, in this case microscopy in the seventeenth century.

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As a historian of science I do adhere to the horribile dictu of ahistorical evolutionary ‘givens’

like cognition in the mind. I wish to be able to historicize the category cognition, let alone

cognitive practices. On the other hand there is no way of escaping the fact that there is an

individual shadow bending over the microscope at the laboratory at night; an individual in a

unique experimental situation. There is no a priori for this kind of practice. But there is

neither an ‘autonomous’ dialogue between robust experimental object and the mindful hand

of the observing scientist.

Experimental cognitivism is realism, albeit with a constructivist cling. Yes, we see through a

microscope, but: what do we see, or rather: how do we end up seeing what we see? In January

1665, the science-afficionado and diarist Samuel Pepys turned out to be unable to “come to

find the matter of seeing anything by my microscope” (Jardine 1999, 43). Johann Franz

Griendel gave evidence for a very special spontaneous generation in his “Micrographia nova"

(1687): Out of a drop of water beneath the magnifying glass the body and the head of a frog

emanates during the time span of three days (Fournier 1996, 153). This is evidently cognition

run wild. But at least the latter example is absurd in a way that it precludes the use of ethical

or transcendental cognitive standards. In Pepys’ case ‘high’ cognitive practices cannot be

involved, because he does not even know how to handle the instrument.

In detail I suggest three types of cognitive practices for microscopy in the seventeenth

century:

Isolating. Select segments of the image of the experimental object. Apprehension of ‘real’

structure and of artifacts.

Modeling. Imaginative forming of 'Gestalts’ of the data imaged

Superimposition. Memory of past experimental episodes

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In this talk I will deal with these cognitive practices focusing on some methodological

remarks of Swammerdam and Leeuwenhoek regarding their microscopes; second, I will turn

to their observations on red blood cells; third, I will take a side-step to Ramón y Cajal and

back to Swammerdam regarding mental models; finally I will turn to superimposition of

mental and ‘real’ images with Swammerdam. Since my approach relies heavily on material

traces of cognitive processes I will deal with Swammerdam’s ‘Nachlass’ which was

purchased by the Niedersächsische Staats- und Universitätsbibliothek Göttingen on the 27th of

September 1784. Even specialists in the field have rarely taken this material into

consideration.

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a

Ever since the biographers Lindeboom and Ruestow Jan Swammerdam, who was born in

1637 and died in 1680, needs to take the tragic part on the stage of the scientific revolution of

the seventeenth century. Although trained in the academic subject of medicine in Leiden

Swammerdam suffered from a precariously modest material basis which in fact was supplied

by his father until the latter’s death. Because Swammerdam inherited part of the estate his

financial difficulties seem to have been eased somewhat for the remaining years of his life.

But there seems to have been another troublesome aspect: Swammerdam was probably

isolated from social life to such a degree that his scientific work served as a sublimation of

this deficit. And Swammerdam was a man of spiritual longing; thus he was caught in the

current of the sect of Madame Bourignon who took to the Netherlands after having been

expelled from France. There is indeed, as his postmortem ‘friend’ and editor Hermann

Boerhaave stated, a basso continuo of worship in his scientific writing, an exhilarated voice

praising the creator. His working style as a scientist did resemble that kind of ardent and

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possibly self-denying rigueur. As Boerhaave describes Swammerdam must have worked

many hours in the sun dissecting specimen and observing them beneath the microscope with

the sweat pouring down his face, spending the nights taking down notes on what he had seen.

Even in Boerhaave's sober report the picture resembles that of a religious martyr.

Still, Swammerdam was a trained academic, and there is, somewhat paradoxically, a host of

allusions, rhetorical topoi, and metaphors adding to the somewhat hypertrophic character of

his letters to the life-long friend Thevenot. Boerhaave who got in possession of the

Swammerdam manuscripts, which Thevenot originally was supposed to publish according to

Swammerdam’s last will, finally managed to edit the material in 1737/1738 under the title

‘Biblia Naturae’. Most of the manuscripts were written between 1665 and 1680, some sixty

years earlier. Boorhaeve did have a hard job. Basically, the material which is preserved

consists of text segments, letters, and copper plates. There is no thematic order in the essays

and treatises. Some letters are written very carelessly and Swammerdam changes abruptly

between French and Dutch, sometimes in the middle of the sentence.

"The first one who used the Tubulus vitreus is a Dutchman, living at Delft, named

Leeuwenhoek, but all he could do with the microscopes concerns only externa, or things he puts

in his glass tubes. It is impossible to go into discussion with him, as he is biased, and reasons in

a very barbarical way, having no academic education” (Lindeboom 1975, 108, Letter 20).

Swammerdam’s insinuating remark regarding the corresponding member of the Royal Society

– Leeuwenhoek –, of course bespeaks his own shortcomings. Leeuwenhoek seems to have

been a much more socially active and successful person, conversing in his native language,

Dutch, with the savants. The illustrations which Leeuwenhoek had done by artisans in

contrast to the ‘draughtsman’ Swammerdam, are perhaps structured more comprehensively.

Leeuwenhoek is regarded up to the present day as a scientist par excellence: passionate,

impartial, scrutinizing, diligent, and incessantly curious.

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b

Both microscopists lay open the construction of their instrument, pointing to Hooke’s lengthy

description in the ‘Micrographia’. Let us turn to Swammerdam first, to be precise a letter to

Thevenot from January 1678 (Lindeboom 1975, 83, Letter 14):

“Nowadays, I believe, the magnifying-glasses are in perfection, and so are the instruments that

one has to use. And I found a very easy way to make all that myself, and I could teach it to

another person in a quarter of an hour. My glasses with which I see the greatest object, are not

greater than as I picture here. But the object should be so near to it that it is nearly touched by

the glass. ".

I believe that you will already have understood how the blood of a man, being outside its veins,

appears as small globuli in this manner. And it remains then still fluid. So that with a

magnifying glass nothing more beautiful is to be seen than that, especially if one lets it run to

and fro, as when every globulus separately is revolving like a circle. One ought to communicate

all these methods and also how one sees this and makes the magnifying-glasses, like you

sometimes say I had promised. However, Sir, a man cannot do everything”.

Illustration 3

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In Dutch even clearer, Swammerdam explicitly states that there is a need to communicate

‚how to see’ with the microscope. „Alle deese manieren en ook hoe men dit siet en de

vergrootg(l)asen maakt, behoorde men te communiceren”. Does the ‘virtuoso-aspect’, the

technical superiority of the instruments answer Hacking’s question: “Do we see through a

microscope”? Not quite. For it is not clear what we see, because

1. There is no theory for the experimental object or the theory is misleading

2. It is still not clear what is ‘real’ regarding the image because of artifacts.

Let us look at Swammerdam’s letter to Thevenot again:

I believe that you will already have understood how the blood of a man, being outside its veins,

appears as small globuli in this manner. And it remains then still fluid. So that with a

magnifying glass nothing more beautiful is to be seen than that, especially if one lets it run to

and fro, as when every globulus separately is revolving like a circle

Leuuwenhoek dealt with erythrocytes – red blood cells – from the beginning of his scientific

career until the end of his life, some fifty years. He examined his own blood, the blood of

frogs and fish, of dogs, cats, and a lot of other mammals. According to the ruling opinion of

his time red blood corpuscles were supposed to be globules, that means round and soft fluid

filled bladders. That is why they were supposed to be spinning especially when they were

isolated from the serum. The point is that healthy erythrocytes in mammals are swollen disks

with a concave depression in the middle of each side; they are not spherical, but oval and flat.

Now, Leeuwenhoek was struck time and time again by precisely this oddity when examining

red blood corpuscles. They seemed to have a nucleus (‘a light’), they seemed to be flat rather

than round. The mindful scientist – and Leuwenhoek's verba cogitandi abound in his letters –

is confronted with the question, if he has to adapt the theory or if the observed phenomenon is

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an artifact. To find out, Leeuwenhoek had his draughtsman depict the microscopic image

directly without his supervision.

Illustration 4

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In the illustration the corpuscles appear with an oval shape. In the right one, which was,

according to Ruestow, supervised by Leeuwenhoek, they are clearly globules. Swammerdam

clearly opts for globules, as far as one can tell from an illustration in Letter 14 and his words

‘revolving like a circle’. The matter, for Leeuwenhoek, remained unsettled. "How one sees

this", as Swammerdam has put it, exactly refers to the cognitive practice of isolating the

relevant segment of the image. In the no-mans-land between lack of theory and unreliable

instrument the microscopist relies on a cognitive practice eventually leading to a sustainable

hypothesis.

d

The neuroanatomist Ramon y Cajal who ‘invented’ the neuron around 1900 had a much better

instrument. The mirror microscope was far superior to the old compound microscope, there

was a device, the camera lucida, which assisted with drawing the image while watching it in

the microscope; and more important, since the 1850s there was a Zeiss-photograph-device

that could be implemented in the microscope. Still, Cajal – the would be artist – drew most of

his specimen as they appeared beneath the microscope or from the photograph or with the

help of the camera lucida. There is evidence that in certain cases he drew the image with his

free right hand while looking into the microscope (Garcia-Lopez, Garcia-Marin, Freire 2010).

It is the drawings he mostly published as illustrations of his findings, not the photographs.

Illustration 5

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When we look at the images we find that the drawings do not identically depict the

photographs. They typify the images, they morphologize them to a structure more readily

discernible. The faithful eye and the mindful hand produce an image more 'objective' than the

photograph. In my terminology, the cognitive practices of isolating and modeling produce a

structure the microscopist can be fairly sure he/she has seen.

Returning to our red blood corpuscles and thus to a period much earlier I think we are

prepared to see now that isolating and modeling in fact are congruent. By isolating segments

of the image the microscopist in fact is modeling. Leeuwenhoek had a wax model of yeast—

globules and of blood corpuscles ready at hand for visitors of his ‘interactive science

museum’ (Taub 1999).

Illustration 6

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One phenomenon that struck me while working with Swammerdam's papers were about eight

copper plates from the ‘Biblia Naturae’-corpus with handwritten commentaries of Boerhaave:

Often segments of the illustration are highlighted with remarks on misrepresented size. Now,

what is amazing here is that Boerhaave is, intentionally, acting as a historiographer and

preserver of texts written fifty years earlier: why does he correct the illustrations according to

the present state of the art whereas Swammerdam’s text, the description is historical? The

answer must be: Boorhaeve doesn’t alter the images with relation to the present state of the

art; he corrects them with regard to what he thinks Swammerdam has seen. Whereas the

singular image of a specimen might have changed according to technical improvements or

skill or environment, the model has essentially remained the same. At least Boerhaave seems

to be certain that he can follow the track of modeling singular phenomena the way

Swammerdam did.

‘Mental models’ in natural philosophy and science? Yes, especially in relation to drawings

which abound in Swammerdam's letters to Thevenot. In Letter 18 Swammerdam describes a

beehive to Thevenot and depicts it.

Illustration 7

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I find that the cells (in Dutch: cellule. My remark) of a beehive are not exactly equally big, but

that they differ often; moreover that in every beehive great irregularities do occur, sometimes

the 'cottages' are twice as long as the others wherein they are collecting honey. Moreover, they

are sometimes curved, and sometimes oblique, and are not always arranged in a regular way;

this all contrary to your concept. However, generally spoken the architecture in it is wonderful,

for example to make a hexagon, they divide a circle (aa) in this manner, equally in six parts, that

sometimes do not differ a whit and then the whole building stands on these admirably regulated

lines by which Archimedes undoubtedly would have been dumbfounded, if he had seen it”

Obviously, the ‘geometrical’ lines, Archimedes would have been dumbfounded by are not on

the microscopic image. Swammerdam adds them to illustrate to his friend what he means by

the ‘architecture’, that is the structure of the object. A single image is transformed into a

model.

e

Let us return to Cajal once more. In the German translation of his “Reglas y Consejos sobre

Investigación Cientifica: Los tónicos de la voluntad" (1897) we read:

“Wenn wir eine wissenschaftliche Aufgabe glücklich zu Ende führen wollen, müssen wir uns

nach Erlernung der zweckdienlichen Methoden in unserem Geiste das Endziel der Frage vor

Augen stellen, um in unserer Gedankenwelt kräftige Strömungen hervorzurufen, also um

zwischen den durch die Beobachtung gewonnenen Bildern und den Gedanken, die in unserem

Unterbewussten schlummern, immer vollständigere und genauere Verknüpfungen herzustellen.

Nur eine äußerste Konzentration unserer Geisteskräfte vermag diese Gedanken in unser

Bewußtsein heraufzurücken" (Cajal 1939, 36)1.

1 The problem of proper translation is aptly demonstrated if we compare the German with the English version of Neely Swanson/Larry W. Swanson: "To bring scientific investigation to a happy end once appropriate methodds have been determined, we must hold firmly in mind the goal of the project. The object here is to focus the train of thought on more and more complex and accurate associations between images based on observation and ideas slumbering in the unconscious – ideas that only vigorous concentration of mental energy can raise to the conscious level". ("Advice to a Young Investigator", p.33).

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It might be useful to step back for a second. What Cajal apparently suggests here (and is

echoed in Poincaré’s and Jacques Hadamard's reflections on innovation in mathematics for

instance) is a leading role for — mental images. Realistic observation is mentally

reconstructed. Models of the observed specimen are remembered, combined with each other

and with altogether different concepts of the ‘subconscious’. That way scientific innovation

takes place.

With Swammerdam there is, in contrast to Leeuwenhoek’s manuscripts, an amazing method

of organizing layers of imagination on the sheet of paper. Thus the cognitive practices are

‘externalized’ on the script carrier whereas Leeuwenhoek ‘verbalizes’ them. Swammerdam’s

letters and manuscripts bare visible marks of the thinking scientist putting fragments of

observation together to epistemic things. As an example for the superimposition of layers of

text (and cognitive practices) I suggest Letter 37 dating from September 1679 (Lindeboom

1975, 156).

Illustration 8

As to the contents of my letter to you four weeks ago: it contained mainly some observations

about the fern which I had made already in the year 1674 and earlier; however, it was neglected

afterwards, please do note that. In my last observations, where I said that the folliculi seminum

are enclosed in some leaflets: that has been written only from a weak memory and although I

looked at it in time; all the small ‘cottages’ were already open, so that I had not all the requisites

at hand that I needed to recognize my error. Now it is like this that the first principles of the

tubercula filicis have the figure of a heart A, which, being like a common membrane or a small

purse, embraces all the follicles equally and hides them. Within this common membrane I have

counted distinctly 178 follicles in some of them. The colour of this ‘tunica investiens' is green in

the beginning, then it gets the colour of muscus on account of the translucent seed ‘cottages’,

and finally it withers, shrinks and bursts. (...) I judge it necessary, Sir, that you add all this to it.”

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Performing an autopsy of the script carrier – the term borrowed from editorial philology

might be in place with the ardent dissectionists here – it is certain that the segment containing

the drawings is of different paper than the rest of the script carrier. Consequently, I think that

the illustrations actually are not drawings, but part of a copper plate inserted in the letter paper

(copper plates needed to be printed on a special kind of paper which is why illustrations

generated by this method in contrast to wood cuts are always presented in special sections of a

book). The demarcation line of copper plate paper and letter paper is clearly discernible on the

original.

If we look at the text we find an apt explanation for this ensemble of material layers.

Apparently, Swammerdam has dealt with seeds of ferns some four years earlier and the

copper plates were made then. After that, the material was ‘neglected’, a formulation

Swammerdam is sure to insert in the text post hoc. So, when Swammerdam writes to

Thevenot in August 1679 about the seeds of fern he communicates his observations from

"swakke memorie" — no small wonder given the fact that the observations took place four

years ago. Also the scientist lacks the ‘requisites' for proper observation, the technical

environment is not suitable “om mijn misslag te erkennen”, “to recognize my error”. At this

point there is a clear mark for a new paragraph on the script carrier; usually, Swammerdam

does not set paragraphs apart. 'Het is dan aldus’, ‘Now it is like this’ introduces the correction

of the bad memory in the ensuing text-depiction-pair. Now, the 'old' observation represented

in the illustration and the ‘new’ observation represented in the text merge. Finally,

Swammerdam takes pains to advise Thevenot to “add all this to it”, that is add the ‘new’

information which was supplied (in part) by the ‘old’ copper plates to the recent faulty

description of the experimental object.

Concluding, I would like to reevaluate shortly what kind of process is taking place here. The

mental images which were accomplished by observation, according to Cajal, are brought in

juxtaposition to the real images preserved in the copper plates. Memory fails, but the material

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traces preserve the objective data. Thus a new combination of material and mental traces

unfolds in the text-depiction-pair. This new combination or model is superimposed on the old

faulty one. An epistemic thing unfolds. It can be seen beneath the microscope.

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References

Cajal, Ramón y: "Regeln und Ratschläge zur wissenschaftlichen Forschung”

München: Reinhardt, 1939.

Fournier, Marian: "The Fabric of Life. Microscopy in the Seventeenth Century", Johns

Hopkins University Press, 1996.

Garcia-Lopez, Pablo; Garcia-Marin, Virginia; Freire, Miguel: "The Histological Slides and

Drawings of Cajal", Frontiers in Neuroanatomy, vol.4, 2010, pp.1-16.

Hacking, Ian: "Do we see through a Microscope?", in: Images of Science. Essays on Realism

and Empiricism, ed. b. Paul M. Churchland, Chicago, 1985.

Jardine, Lisa: "Ingenious Pursuits: Building the Scientific Revolution", London, 1999.

Lindeboom, J.A.: "The Letters of Jan Swammerdam to Thevenot", Amsterdam: Swets &

Zeitlinger, 1975.

Ruestow, Edward G.: "The Microscope in the Dutch Republic. The Shaping of Discovery",

Cambridge, 1996.

Taub, Liba: "Heroes of Microscopy and Museology", Studies in the History and Philosophy of

Science, vol.30, nr.4, 1999, pp.729-744.

Wilson, Catherine: "The Invisible World. Early Modern Philosophy and the Invention of the

Microscope", Princeton, 1995.