In the last post, we talked about objectivity as a scientific ideal aimed at building a reliable picture of what the world is actually like. We also noted that this goal travels closely with the notion of objectivity as what anyone applying the appropriate methodology could see. But, as we saw, it takes a great deal of scientific training to learn to see what anyone could see.
The problem of how to see what is really there is not a new one for scientists. In her book The Scientific Renaissance: 1450-1630 , Marie Boas Hall describes how this issue presented itself to Renaissance anatomists. These anatomists endeavored to learn about the parts of the human body that could be detected with the naked eye and the help of a scalpel.
You might think that the subject matter of anatomy would be more straightforward for scientists to see than the cells Fred Grinnell describes  (discussed in the last post), which require preparation and staining and the twiddling of knobs on microscopes. However, the most straightforward route to gross anatomical knowledge - dissections of cadavers - had its own challenges. For one thing, cadavers (especially human cadavers) were often in short supply. When they were available, anatomists hardly ever performed solitary dissections of them. Rather, dissections were performed, quite literally, for an audience of scientific students, generally with a surgeon doing the cutting while a professor stood nearby and read aloud from an anatomical textbook describing the organs, muscles, or bones encountered at each stage of the dissection process. The hope was that the features described in the text would match the features being revealed by the surgeon doing the dissecting, but there were doubtless instances where the audio track (as it were) was not quite in sync with the visual. Also, as a practical matter, before the invention of refrigeration dissections were seasonal, performed in the winter rather than the warmer months to retard the cadavers decomposition. This put limits on how much anatomical study a person could cram into any given year.
In these conditions, most of the scientists who studied anatomy logged many more hours watching dissections than performing dissections themselves. In other words, they were getting information about the systems of interest by seeing rather than by doing - and they werent always seeing those dissections from the good seats. Thus, we shouldnt be surprised that anatomists greeted the invention of the printing press by producing a number of dissection guides and anatomy textbooks.
Whats the value of a good textbook? It shares detailed information compiled by another scientist, sometimes over the course of years of study, yet you can consume that information in a more timely fashion. If it has diagrams, it can give you a clearer view of what there is to observe (albeit through someone elses eyes) than you may be able to get from the cheap seats at a dissection. And, if you should be so lucky as to get your own specimens for study, a good textbook can guide your examination of the new material before you, helping you deal with the specimen in a way that lets you see more of what there is to see (including spatial relations and points of attachment) rather than messing it up with sloppy dissection technique.
Among the most widely used anatomy texts in the Renaissance were uncorrupted translations of On the Use of the Parts and Anatomical Procedures by the ancient Greek anatomist Galen, and the groundbreaking new text On the Fabric of the Human Body (published in 1543) by Vesalius. The revival of Galen fit into a pattern of Renaissance celebration of the wisdom of the ancients rather than setting out to build "new" knowledge, and Hall describes the attitude of Renaissance anatomists toward his work as Galen-worship. Had Galen been alive during the Renaissance, he might well have been irritated at the extent to which his discussions of anatomy - based on dissections of animals, not human cadavers - were taken to be authoritative. Galen himself, as an advocate of empiricism, would have urged other anatomists to dissect with a fresh eye, attentive to what the book of nature (as written on the bodies of creatures to be dissected) could teach them.
As it turns out, this may be the kind of thing that's easier to urge than to do. Hall asks,
[W]hat scientific apprentice has not, many times since the sixteenth century, preferred to trust the authoritative text rather than his own unskilled eye? (137)
Once again, it requires training to be able to see what there is to see. And surely someone who has written textbooks on the subject (even centuries before) has more training in how to see than does the novice leaning on the textbook.
Of course, the textbook becomes part of the training in how to see, which can, ironically, make it harder to be sure that what you are seeing is an accurate reflection of the world, not just of the expectations you bring to your observations of it.
The illustrations in the newer anatomy texts made it seem less urgent to anatomy students that they observe (or participate in) actual dissections for themselves. As the technique for mass-produced illustrations got better (especially with the shift from woodcuts to engravings), the illustrators could include much more detail in their images. Paradoxically, this could be a problem, as the illustrator was usually someone other than the scientist who wrote the book, and the author and illustrator were not always in close communication as the images were produced. Given a visual representation of what there is to observe and a description of what there is to observe in the text, which would a student trust more?
Bruce Bower discusses this sort of problem in his article Objective Visions,  describing the procedures used by Dutch anatomist Berhard Albinus in the mid-1700s to create an image of the human skeleton. Bower writes:
Albinus carefully cleans, reassembles, and props up a complete male skeleton; checks the position of each bone in comparison with observations of an extremely skinny man hired to stand naked next to the skeleton; he calculates the exact spot at which an artist must sit to view the skeletons proportions accurately; and he covers engraving plates with cross-hatched grids so that images can be drawn square-by-square and thus be reproduced more reliably. (360)
Here, it sounds like Albinus is trying hard to create an image that accurately conveys what there is to see about the skeleton and its spatial relations. The methodology seems designed to make the image-creation faithful to the particulars of the actual specimen -- in a word, objective. But, Bower continues:
After all that excruciating attention to detail, the eminent anatomist announces that his atlas portrays not a real skeleton, but an idealized version. Albinus has dictated alterations to the artist. The scrupulously assembled model is only a spingboard for insights into a more "perfect" representation of the human skeleton, visible only to someone with Albinus anatomical acumen. (360)
Here, Albinus was trying to abstract away from the peculiarities of the particular skeleton he had staged as a model for observation in order to describe what he saw as the real thing. This is a decidedly Platonist move. Platos view was that the stuff of our world consists largely of imperfect material instantiations of immaterial ideal forms - and that science makes the observations it does of many examples of material stuff to get a handle on those ideal forms.
If you know the allegory of the cave, however, you know that Plato didn't put much faith in feeble human sense organs as a route to grasping the forms. The very imperfection of those material instantiations that our sense organs apprehend would be bound to mislead us about the forms. Instead, Plato thought we'd need to use the mind to grasp the forms.
This is a crucial juncture where Aristotle parted ways with Plato. Aristotle still thought that there was something like the forms, but he rejected Plato's full-strength rationalism in favor of an empirical approach to grasping them. If you wanted to get a handle on the form of "horse," for example, Aristotle thought the thing to do was to examine lots of actual specimens of horse and to identify the essence they all have in common. The Aristotelian approach probably feels more sensible to modern scientists than the Platonist alternative, but note that we're still talking about arriving at a description of "horse-ness" that transcends the observable features of any particular horse.
Whether youre a Platonist, an Aristotelian, or something else, it seems pretty clear that scientists do decide that some features of the systems theyre studying are crucial and others are not. They distinguish what they take to be background from what they take to be the thing theyre observing. Rather than presenting every single squiggle in their visual field, they abstract away to present the piece of the world theyre interested in talking about.
And this is where the collaboration between anatomist and illustrator gets ticklish. What happens if the engraver is abstracting away from the observed particulars differently than the anatomist would? As Hall notes, the engravings in Renaissance anatomy texts were not always accurate representations of the texts. (Nor, for that matter, did the textual descriptions always get the anatomical features right -- Renaissance anatomists, Vesalius included, managed to repeat some anatomical mistakes that went back to Galen, likely because they "saw" their specimens through a lens of expectations shaped by what Galen said they were going to see.)
On top of this, the fact that artists like Leonardo Da Vinci studied anatomy to improve their artistic representations of the human form spilled back to influence Renaissance scientific illustrators. These illustrators, as much as their artist contemporaries, may have looked beyond the spatial relations between bones or muscles or internal organs for hidden beauty in their subjects. While this resulted in striking illustrations, it also meant that their engravings were not always accurate representations of the cadavers that were officially their subjects.
These factors conspired to produce visually arresting anatomy texts that exerted an influence on how the anatomy students using them understood the subject, even when these students went beyond the texts to perform their own dissections. Hall writes,
[I]t is often quite easy to "see" what a textbook or manual says should be seen. (141)
Indeed, faced with a conflict between the evidence of ones eyes pointed at a cadaver and the evidence of ones eyes pointed at an anatomical diagram, one might easily conclude that the cadaver in question was a weird variant while the diagram captured the standard configuration.
Bowers article describes efforts scientists made to come up with visual representations that were less subjective. Bower writes:
Scientists of the 19th century rapidly adopted a new generation of devices that rendered images in an automatic fashion. For instance, the boxy contraption known as the camera obscura projected images of a specimen, such as a bone or a plant, onto a surface where a researcher could trace its form onto a piece of paper. Photography soon took over and further diminished human involvement in image-making. Researchers explicitly equated the manual representation of items in the natural world with a moral code of self-restraint. A blurry photograph of a star or ragged edges on a slide of tumor tissues were deemed preferable to tidy, idealized portraits. (361)
Our nave picture of objectivity may encourage us that seeing is believing, and that mechanically captured images are more reliable than those rendered by the hand of a (subjective) human, but its important to remember that pictures - even photographs - have points of view, depend on choices made about the conditions of their creation, and can be used as arguments to support one particular way of seeing the world over another.
In the next post, we'll look at how Seventeenth Century natural philosophers labored to establish a general-use method for building reliable knowledge about the world, and at how the notion of objectivity was connected to these efforts, and to the recognizable features of "the scientific method" that resulted.
 Marie Boas Hall, The Scientific Renaissance: 1450-1630. Dover, 1994.
 Frederick Grinnell, The Scientific Attitude. Guilford Press, 1992.
 Bruce Bower, "Objective Visions," Science News. 5 December 1998: Vol. 154, pp. 360-362