Microscopy by induction - historically, did anyone reason along these lines?

Before the first use of the microscope to investigate microscopic life in ~1650, was there anyone who reasoned as follows?

“There are animals and plants ranging over all sizes, from huge down to as small as I can see with my naked eye. There’s no particular reason why the graduation of sizes should stop at the limit of human vision, therefore there’s almost certainly life that’s smaller than I can see.”

This would seem a fairly natural line of thought, to me. And yet the discovery of microscopic life in 1676 by Van Leeuwenhoek seems to have come as an utter shock to everyone:

I was just wondering if anyone prior to Van Leeuwenhoek thought along those lines, does anyone here know?

I take issue with the line you quoted in bold. It’s not so much that they were skeptical about single-celled organisms, as if to say that they believed only in multiple-celled organisms. Rather, the whole concept of a cell was foreign to them.

More than that, the whole concept of a microscopic world was foreign to them. We are so used to it that the OP seems to be a reasonable question. But from their point of view, it was ridiculous. Their logic was more like, “If you can’t see it, it doesn’t exist.” That idea had worked for thousands of years, and it took a long time for the new concepts to take hold.

Or “if you can’t see it, it’s invisible” (which even makes sense) - thus, diseases were caused by vapours, evil spirits, etc. And when food spoiled, moulds, maggots etc arose from it spontaneously, because the causal agent was not obvious.

Hmm. I recall that some thought sperm must contain tiny human beings that would only grow in a woman’s womb. If there were people believing that then they probably believed in creatures too small to see, but probably didn’t concieve of things like single cell life forms.

The homunculus-in-sperm notion arose after spermatozoa had been observed with a microscope and described.

Before that, I think it was generally understood that semen was some kind of ‘seed’ (indeed, that the male was the only contributor to conception), but the cellular nature of it was not known.

I wonder if people understood that human vision had limits along those lines until they were demonstrated with the microscope - if they actually understood that something could be so small that the human eye couldn’t see it. That’s not an easy concept to jump to unless you can see it demonstrated.

magnetism was due to really small screws.

The ancient Greeks had a theory of atoms (the word atomos means 'indivisible in Greek)- so they were OK with the notion of something small below the limit of vision (or at least I think so).

I’d think it would be pretty small jump of logic that there could be something smaller that you can see, for the simple reason that people’s eyesight varies- Grandma can’t see that big fly buzzing round the room, Mum can’t see the smallest aphids on the plants, so gets me to check for them; I wonder if there’s bugs so small I can’t see them?

It gets even more obvious as your eyesight deteriorates with age, as you know that there’s things there that you used to be able to see, and now you can’t. It could well be suprising just how small living things can be, but that they could be smaller than you could see really couldn’t be that much of a shock.

Sure, and with small bugs (well, things in general) it’s easy to notice that there are details that you’d like a better look at - and that desire drove the invention of magnifying optics.

Moreover, there was tons of study of and speculation over unseen life forms in the Middle Ages, but it was in the realm of theology, rather than anything we would recognize as science.

Jainism believed that the universe was full of things too small to be seen, but that was more of a “hurt nothing” philosophy than a scientific belief.

During the time of Julus Caesar the Roman scholar Marcus Terentius Varrowarned about swamps because they were home to “certain minute creatures which cannot be seen by the eyes.”

Of course the problem with having bold insights more than 1,600 years before they can be proven is that people forget you had them in the first place.

I think what people are missing is religion. If God made the universe and everything in it for humans, then it makes no sense for there to be things no human can see. People were burned as here ics for suggesting the stars were other suns, for similar reasons.

Cite that this was a widespread belief, please.

While the line I bolded said “single celled organisms” (and so may have been a distraction), what I was actually thinking about in the OP was “organisms smaller than I can see”.

I’m doubting there was an active logical position like that, are you aware of anyone actually positing it? I could more easily believe that no-one had ever happened to think along those lines, that anyone had and dismissed it for that reason.

They would have known that some creatures were so small they were hard to see, and the knew some people had worse eyesight than others. **Filbert’s **post is very good here: “I used to be able to see fleas and bedbugs, now I can’t. Perhaps there always were creatures I couldn’t see?”.

I don’t know how widespread it was but I’ve heard this argument as well. It supposedly was one of the arguments raised against Galileo when he reporting seeing moons orbiting Jupiter with his telescope.

There’s a poem going back to 1733 wondering if the phenomenon of big animals having smaller parasites can be extended indefinitely:



This can be thought of as another example of the Droste effect:


It’s claimed that the following triptych from 1320 is an example of this. I can’t see the smaller example of it within this picture well enough to tell what’s going on here. The smaller example is in the center panel. It’s being handed from the person kneeling on the left to the person in the center:


I can’t find any evidence that the Galileo affair was about whether things that couldn’t be seen except with the telescope didn’t exist:


The Galileo affair, as has to be explained every time it comes up here, was more about politics than about science.

I would argue the contrary. With small bugs, it’s easy to notice that there are details you don’t want a better look at. Like, really don’t.

I’ll point out that this kind of reasoning by induction fails utterly going the other way: despite the range of animal sizes, there are no animals so large that humans cannot see them.