Here is my answer to the question: In what sense did the images provided by the early modern microscope explain anything?
I believe that the images provided by the early modern microscope explained (in part) a great variety of phenomena. Perhaps, though, ‘explained’ is a strong word that indicates a greater role for the microscope than it indeed played. Instead of the microscope as ‘explanatory’ I think it would be better to characterize its role as lending support to a wide variety of theories in a number of different disciplines: from philosophy and theology to physiology and biology. For instance, microscopic observations were used to support:
1. Rationalist and Idealist/Empiricist philosophies (Malebranche and Berkeley)
The rationalist philosopher Nicholas Malebranche used microscopic observations in order to further his philosophical stance that certain knowledge can be gained only through the process of ratiocination, which is grounded in God's greatness. Strangely, Malebranche uses (with certainty) microscopic observations (that is, observations which are empirical) to further an argument against the possibility that such observations can be certain! He states that, “only the intelligible can through its evidence and light supply food for intelligent minds” (251 Malebranche) . But then he proceeds to use microscopic evidence and essentially refute in practice what he has said theoretically:
I began to read a book which I had with me, and I found therein a very astounding thing, namely, that there is in the world an infinite number of insects at least a million times smaller than the one I had just been examining, fifty thousand times smaller than a grain of sand… These philosophers are very glad that the facts they put before us can be verified at any time, and that people are able to appreciate with certainty the multiplicity and delicacy of the wonderful works of the author of the universe. (252-253 Malebranche).
So, even though using empirical data from the realm of microscopy contradicts what he is attempting to illustrate (that we cannot gain certain knowledge from our senses, and thus, from the microscope) Malebranche does so anyway! I think this is interesting, because it shows us how convincing (or at least impressive) the observations from the microworld were in the early modern period; so convincing that Malebranche felt he had to include them in order to strengthen his argument.
In addition to the rationalist’s (irrational?) utilization of the microscope, George Berkeley used the microscope to further his own idealistic philosophy. Berkeley is almost diametrically opposed to Malebranche, in that he believes that our existence is not founded on rationality, but on our being perceived. For Berkeley, to be is to be perceived. But his adoption of microscopic observations was much more specific than Malebranche’s: he used the microscope (among other examples) to show that Locke’s distinction between primary and secondary qualities cannot hold (423-424 Berkeley).
2. Anti-spontaneous theories of generation
One of the expectations from the microscope was that it might settle the debate about generation (for example: where do the maggots on rotting meat come from, how does fermentation occur, etc.). There were two sides to this debate. One believed that the maggots (or the fermentation, etc.) were the result of some sort of spontaneous generation, due to a vegetative force (Needham) or, later, some sort of chemical process (Leibig). The other side thought that generation was never (and could not be) spontaneous, and that all generation could be explained by animal/bacterial or plant reproduction. Thus, early experiments in favor of spontaneous generation (Needham’s hermetically sealed mutton gravy) were seen as instances of poor experimental procedure by the anti-spontaneity camp. Surprisingly, definitive evidence could not be provided for either side until much later than expected (dates vary, but certainly by Pasteur in 1857). In the mean time, the microscopic evidence provided by the anti-spontaneists began tilting the scales steadily toward their position.
In the first half of the 19th century, the anti-spontaneists used microscopic observations of yeast to illustrate that fermentation was not a simple chemical process (and thus, that life did not emerge spontaneously), but the work of small plant-like globules (yeast). Cagniard-Latour elaborates:
The principal results of the present work are: (1) The beer yeast is a mass of small globules which are able to reproduce, and consequently are organized, and are not a simple organic or chemical substance, as has been supposed…” (23 Cagniard-Latour).
He achieved his results through the use of a microscope which “enabled him to obtain enlargements of 300-400 times.” (20 Cagniard-Latour). Schwann obtained similar results, using similar methods to Cagniard-Latour: “Microscopic examination of the beer yeast showed the familiar little grains which the ferment forms…it is without a doubt a plant” (18, Schwann).
3. Spermist (animalculist) ideas about preformation
There was also a lot of optimism in the early modern period that the microscope would be helpful in the physiological debate about how children are formed (that is, how life emerges from the womb). A popular theory (for theological reasons) was the doctrine of preformation which stated that all future living creatures were created in the instant of creation (about 7000 years ago). Thus, every human being that would ever exist was, in some way, completely formed in either Eve's ovaries or Adam's testicles (depending on whether you were an ovist or a spermist).
The support provided by the microscope for the spermist (or as it is sometimes called, animalculist) doctrine of preformation is best illustrated by Leeuwenhoek in a letter to William Brounker about the constitution of semen:
As regards the parts themselves of which the denser subtance of the semen is mainly made up, as I have many times observed with wonder, they consist of all manner of great and small vessels, so various and so numerous that I have not the least doubt that they are nerves, arteries and veins… (293,295 Leeuwenhoek).
This is an odd case indeed, as the editor Dobell has noted. We now know (with the aid of more powerful microscopes) that there could not have been veins or arteries in the sperm that Leeuwenhoek was examining. This seems to be a case where the theory has affected the evidence that attempts to prove that theory: Leeuwenhoek believed in preformation, and, thus, his experiments/examinations led him to the conclusion (one that he wanted to hear) that preformation was in fact true. Leeuwenhoek in fact seems to (somewhat indignantly) defend himself against objections that his observations cannot be repeated (335, 337 Leeuwenhoek). Though we may now ask the question as to whether or not this is a case of ‘explanation’ of a phenomenon or manipulation, clearly, at the time their was no better evidence available with which to measure Leeuwenhoek’s claim.
4. Theological and Cosmological ideas
A number of theological ideas found support in the new worlds opened up by the microscope. We have already seen that preformation (which has its roots in the Christian account of creation) found support in the microscope. But, other biblical interpretations were attacked using microscopic support. In Joseph Glanville’s book The Vanity of Dogmatism he argues that before the fall, Adam had perfect senses. That is, he was able to experience the world exactly as it was, from the tiniest hair on a mite’s leg, to the faintest whisper. After his exile from the garden, however, Adam lost this direct connection to the ‘real’ world, and had the imperfect senses that we now have. Henry Power denied this interpretation in the preface to his Experimental Philosophy:
Neither do I think that the Aged world stands now in need of Spectacles, more than it did in its primitive Strength and Lustre: for howsoever though the faculties of the soul of our Primitive father Adam might be more quick and perspicacious in Apprehension, than those of our lapsed selves; yet certainly the Constitution of Adam's Organs was no divers from ours, nor different from those of his Fallen Self, so that he could never discern those distant, or minute objects by Natural Vision, as we do by the Artificial advantages of the Telescope and Microscope… (Preface, Power)
So here Power is using the microscope to claim that we now have more knowledge about the world than Adam could ever have possibly had. He uses the worlds opened up by the microscope (and the telescope) to illustrate that, far from becoming more and more distant from God’s creation, we are becoming ever closer to understanding it. Robert Hooke has similar notions about the cosmological role of the microscope. He states in the preface to his Micrographia that:
The next care to be taken, in respect of the Senses, is a supplying of their infirmities with Instruments, and, as it were, the adding of artificial Organs to the natural; this in one of them has been of late years accomplisht with prodigious benefit to all forms of useful knowledge, by the invention of Optical Glasses… by the help of Microscopes, there is nothing so small, as to escape our inquiry; hence there is a new visible World discovered to the understanding (3-4 Hooke)
Like Power, Hooke is proposing that with the help of these “artificial organs” we can discover new worlds, and come to understand the true nature of reality more closely.
So, though I do not believe that the microscope by itself ‘explained’ anything, I do believe that it was used to further solidify larger explanations for a wide variety of phenomena, with varying degrees of importance. For instance, the role that the microscope played in the philosophy of Malebranche was decidedly (and necessarily) minimal, but, it played a huge part in deciding between theories of generation. It seems that without the support lent to biological/physiological theories, debates may have continued for much longer over the ‘true’ nature of the phenomena. Though it seems the role microscopic observations were not decisive in philosophical debates, a case could possibly be made to the contrary (possibly through a more detailed philosophical analysis of both Hooke and Power).
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