Go back to article: A symposium on histories of use and tacit skills

Peter Heering: Analysing experiments with the replication method

Analysing experiments with the replication method is normally constituted by three closely interwoven steps – the reconstruction of the apparatus (or the set-up), the re-enactment of the experiment, and the contextualisation of the experiences made. In this respect, this case study on solar microscopes is somewhat unusual as most experiences were made with original instruments that belong to the collection of the Deutsches Museum Munich (Heering, 2008; Heering, 2009). Even though I afterwards did some work with a reconstructed solar microscope, the discussion will mainly focus on the experiences in Munich.

Solar microscopes are projection devices that were rather popular in the second half of the eighteenth century and which are closely connected to the experimental culture of the Enlightenment. The instrument uses sunlight reflected with a mirror on to a condensing lens. This light illuminates the microscopic specimen that is placed close to the focal point of the lens. The image of the specimen is projected via a lens or a lens system on to a screen. The instrument is used in a darkened chamber; it is placed in the shutter of a window so that the mirror is outside the room. The popularity of the instruments cannot be inferred from printed sources only, even though solar microscopes are found in most eighteenth-century instrument makers’ catalogues as well as in textbooks. Also, the number of instruments that still exist and are kept in museum collections may serve as an indication of their popularity. To give a few examples: the Science Museum and Rijksmuseum Boerhaave each have more than 35 instruments; the Museum for the History of Science Oxford has 45. Moreover, when looking at contemporary accounts, eighteenth-century natural philosophers are very positive about the potential of the instrument. To give just one example: Joseph Priestley wrote that ‘…the image or picture of the object is thrown distinctly and beautifully upon a screen of white paper, and may be magnified beyond the imagination of those who have not seen it’ (Priestley, 1772, p 742). This statement presents an interesting problem to the historian of science – when the magnification is beyond the imagination of those who have not seen it, this makes it challenging to estimate the performance of the device. To make things worse, a different characterisation can be found in publications from the nineteenth century. ‘The image of a common solar microscope may be considered as a mere shadow, fit only to amuse women and children [...] The utmost it can do is to give us the shadow of a flea, or a louse as big as a goose or a jackass...’ (Goring, 1827, in Altick 1978, p 369).

This was one of the starting points of my research with instruments at the Deutsches Museum. Among the instruments kept in the collection was one device signed ‘Dollond’ that dates from around 1780 (see Figure 5), and another by Junker that dates from around 1791 (see Figure 6). Both instruments had sliders with the accompanying specimens still in existence. Whilst Dollond’s instrument can be seen as state of the art, Junker’s instrument is technically less sophisticated – this is related to Junker’s intention: he wanted to build a solar microscope that would be substantially cheaper and could be used in schools (Heering, 2011).

Figure 5

Colour photograph of a robustly made brass solar microscope

Dollond solar microscope in the collection of the Deutsches Museum München

Figure 6

Colour photograph of a simple wooden solar microscope

Junker solar microscope in the collection of the Deutsches Museum München. The cardboard tube was missing and replaced by the workshops of the museum

Replication was needed to compare the experience each instrument gave. Once I had made a room completely dark (which itself turned out to be a challenge), I started working with the instruments and immediately realised that indeed the images are very bright, and very large (see Figure 7). I also realised that the visual impression cannot be communicated in words – one has to see the images in order to understand the visual potential of these devices. This was not just my impression but also part of the feedback I received when I started doing demonstrations for audiences. This activity was evaluated with questionnaires; one was used prior to the demonstration to address expectations, the other immediately afterwards to assess the actual experiences. The impressiveness of the effect is also evident in Elizabeth Cavicchi’s 2008 account of the demonstration she attended: ‘Even Cuff’s evocative and promotional words are inadequate to describe what it was like when sunlit images from Dollond’s brass tube filled the fabric screen in our dark lab. Minute relics of the microscopic past were projected to human-sized height while retaining crisply edged detail and brilliance as if possessed of dimensions comparable to our own. What we saw, lit up with lacework shadows, was astonishing. The effect was as startling as if seeing something so enlarged were novel…’ (Cavicchi, 2008, p 374). It appears to be remarkable that people in the twenty-first century are still affected by these images, but this is not the line of argument I am going to follow here.

Figure 7

Colour photograph of a solar projection of a mounted insect wing

Solar microscope projection of an insect’s wing

Instead, I will discuss some of the results of the contextualisation that developed out of the experiences made with the solar microscope. When looking into the eighteenth-century literature about microscopy, a number of accounts were striking to me, accounts such as the following one by the Augsburg instrument maker Brander: ‘What can be more pleasant and more appealing but when we – even without stepping out of our parlour – seemingly catch sight of a new world, or at least of completely new inhabitants, that were up to now entirely unknown to us? Our attention will be most excited when we encounter at an innumerable amount of midget animalcules in the smallest drop of water the same order, that we observe in the macroscopic and even in the entire cosmos’ (Brander, 1769, Vorbericht, n.p.).

Such a description does not correspond with what I experienced with the solar microscope. According to Brander’s description, the instrument stands between the observer and the microcosm – it may be seen as a mediator between the two worlds but at the same time separates the observer from the inhabitants of the microcosm. Yet this is completely different with the solar microscope: here, we have an instrument that creates a particular space in which humans can meet the inhabitants of the microcosm (see Figure 8). This space is no longer part of the outside world, which gets evident as soon as it gets dark. This happens when a cloud moves between the Sun and the mirror, thus blocking the sunlight. One immediately realises that something has happened outside, but cannot tell whether it is worth standing in darkness and waiting for the light to reappear (when the cloud does not block it anymore), or whether the projection time is over.

Figure 8

Colour photograph of a solar projection of a mounted flea being shown to an audience via projector

Demonstration of a solar projection of a flea

Yet more important appears to be that the created space enables an encounter with the inhabitants of the microcosm – this perception can also be found in historical sources: ‘To see this well-known small animal, I mean the flea, alive in the above-mentioned size [of a lion or an elephant, P H], arouses particularly for the fair sex no little pleasure. They laugh at his quaint shape, in which it appears. They point a finger at it, and, when they exclaim sarcasms against this miserable, they taste the sweetness of revenge for the mischief it did to them. Now they see finally how terrible their hereditary enemy is, whom they have known that long’ (Anon, 1781, p 460).
It appears that – according to this quotation – the audience of this demonstration actually address the flea and act as if in a zoo, watching and interacting with the animal in its cage. In this respect, another difference between the solar and the common microscope appears to be relevant: the common microscope requires the development of skills in order to be able to make observations of the microcosm. Here a distinction used by Ludwik Fleck (1986) may be helpful. Fleck distinguishes between ‘looking’ and ‘seeing’ – the former referring to the physiological process of visual perception, the latter to the cognitive aspect of identifying what someone is looking at. In this terminology, it is possible for the unskilled observer to look at microscopic specimens without any prior practice as one can simply look at the image on the wall – this is not the case with a common microscope. However, the ordinary microscope requires that people learn to see – and here lies a particular potential of the solar instrument, which becomes especially effective in demonstrations. The instrument enables novices to learn to see the microscopic world, and this becomes evident once it is used with an audience. This quality has also been explicit in the eighteenth-century accounts: ‘Besides this particular Property it hath, that the Numbers of People may view an Object at the same Time, and may point to different Parts thereof, and by discoursing on what they see, may understand each other better, and more probably find out the Truth, than when they are obliged to look one after the other’ (Adams 1747, p 11).

From my understanding, emphasis should be placed on the educational aspect of the demonstrations– looking at the same time as others is a requirement for an efficient mode to ‘find out the truth’ collectively.[1] In the above quotation, two aspects that are relevant for the role of the solar microscope in the eighteenth century can be identified: on the one hand, it enabled users (and this includes the audience who are looking at the projections) to develop an ability for seeing microscopic specimens without taking the pains to learn how to look at them. This educational potential meets a requirement for microscopy that has been identified, e.g. by Jutta Schickore: ‘The observer’s mental activities were understood to be one major factor conditioning the outcome of microscopical investigations. […] If the observers exerted strict control over their mental operations, they could prevent erroneous results’ (Schickore, 2001, p 128). At the same time, this use of the solar microscope met a social requirement of the Enlightenment: as Walters (1997) has already observed, ‘polite science explicitly associated the study of natural philosophy with conversation, the fundamental activity of polite society’ (Walters, 1997, p 126). In this respect, as Walters observed, solar microscopes met these standards: ‘Since the solar microscope…projected images of microscopic objects onto a screen, they did not suffer from the social disadvantages of traditional microscopes. Indeed, solar microscopes strongly encouraged common observation’ (Walters, 1997, p 141).

It appears to be the combination of these aspects of the looking experience that explain the success of these instruments. Another aspect can be discovered from the projection of crystallisations, or the shooting of crystals: here, as Ledermüller puts it, the demonstrator can place ‘the most secret work of nature’ before the observer’s eyes. A drop of salt solution is placed on an empty glass in the slider and placed in the instrument. As the water evaporates, the crystals are formed. These demonstrations are particularly suited for projection with the solar microscope as the dynamic development can also be seen collectively; this would not be possible with a common microscope. Yet, when re-enacting these experiences, it was striking to me how slowly the crystallisation took place.

Video 1

Projection of salt crystallising on a glass slide

Sequence from the projection of a crystallisation

The term ‘shooting’ gave me the impression that this is a rapid process, but as one can see, this is not the case. In this respect, the re-enactment serves as a corrective to the understanding that may have developed from the analysis of the sources. From these experiences, but also from others, I would argue with the statement that ‘understanding past practice is enshrouded in certain failure due to the fact that different representations of a perceptual experience cannot capture the original lived one. We suggest, however, that archival resources can offer rich insights into past practices’ (Harris and Van Drie, 2015, p 109). This is not to say that archival resources do not offer rich insights; in this respect, I am not opposing the statement of Harris and van Drie. However, I suggest that practical experiences benefit from these insights, and the archival insights in turn, benefit from the practical experiences. 

Component DOI: http://dx.doi.org/10.15180/170808/003