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Imagine you have someone sent back in time without warning. He is smart and has a good generalist grasp of science and technology, but is not a master of any particular field. He wants to use a crude microscope, for instance to demonstrate the presence of germs and thus germ theory.

At what point in history would our mechanical and glass shaping skills be sufficiently advanced to build a rudimentary microscope given only a general explanation of concave mirrors 'stacked' on each other? Assuming that they had sufficient funding from an interested source to cover reasonable expenses and time to try a few failed attempts before the final product? Could this be managed during the middle ages?

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    $\begingroup$ Am I the only one that thinks "I should learn how to make X, just in case I ever end up back in time..."? I may have to add lenses to the list. $\endgroup$ – AndyD273 Mar 17 '15 at 14:13
  • $\begingroup$ @AndyD273 I actually have thought that lol. Even more important was "I should keep X electronic devices on my at all times just in case I go back in time, so I can use them to reinvent science" There is a reason I still wear a watch with a stopwatch feature, do you know how major that will be in feudal japan for generating constants!? $\endgroup$ – dsollen Mar 17 '15 at 14:25
  • $\begingroup$ I had never thought how useful a stopwatch would be in feudal Japan, actually... It makes me curious, but searching "feudal japan constants" brings up "Feudal Japan was in a constant state of war..." a bunch of times. I'm trying to limit my list to things I could do without electricity, just in case. $\endgroup$ – AndyD273 Mar 17 '15 at 15:33
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    $\begingroup$ Feudal Japan was just a random time period. but having a time keeping device that is accurate to miliseconds would be very useful, particularly if it's in a place that doesn't use either Metric or English system, meaning none of the constants I have memorized, like Gravity, are any good to me. I would need to recreate them somehow. And a watch will run for many many years, long enough to get in re-generate constants I need. Though...if I had a ruler with me between those two I could just translate foreign units to metric to begin with... $\endgroup$ – dsollen Mar 17 '15 at 15:55
  • $\begingroup$ Actually, even to this day, high-precision lenses are made with very 'basic' techniques (just do an image google search on 'lens grinding') since this reduces systematical errors, so basically grinding some glass and stone together in a circular motion should give you a workable lens. $\endgroup$ – Sanchises Mar 18 '15 at 14:34
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You don't need perfectly ground lenses to make a microscope, much less the advanced optics knowledge to build compound, stacked lenses, modern microscope.

This is Antonie van Leeuwenhoek's microscope (the first microscope in the world):

World's first microscope

The lens is just a glass sphere, nothing complicated. The slide is just a pin.

With this he was able to discover:

  • cells
  • bacteria
  • sperm
  • the fact that microorganisms eat each other just like larger animals
  • the fact that microorganisms reproduce (it was popular theory back then that microorganisms spontaneously appear - like dust that suddenly come alive due to some chemical process)

Some of his lab reports read like a Discovery Channel documentary of lions and zebras.

Interestingly, people who tried to reproduce Leeuwenhoek's microscope (including some who wanted to be his competitor at the time and sell microscopes) didn't manage to produce his lenses via grinding. He never patented his lens making technique and kept it a secret. People later managed to reproduce his lenses by taking thin glass threads and melting the ends letting the glass form beads.

So to build your first microscope, all you need is a glass blower competent enough to work with very-very fine glass threads.

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    $\begingroup$ very good comment. But if I read it correctly it sounds to me that if I went to a middle age's glass maker and described what I think of as a microscope he would struggle and likely fail to make it? after all he would attempt the grinding lens approach because that is what a laymen would suggest. How hard would it be to figure out to try the above approach to a competent glass blower when grinned lens failed? Would lack of knowledge of this type of microscope prevent building one until better lens grinding was available? $\endgroup$ – dsollen Mar 17 '15 at 18:33
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    $\begingroup$ That's the cheat sheet: knowing that grinding doesn't work for the tech/skill available at the time. But glass blowers have been making glass balls and marbles. All you need is someone to realize that if you make a small enough marble you'd have a lens. Or, in an alternate history scenario, someone who's a Leeuwenhoek and/or microscope geek to go back in time (he'd probably know about the bead thing) $\endgroup$ – slebetman Mar 17 '15 at 18:38
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    $\begingroup$ Ironically, it's easier to come up with a scenario of a hobbyist glass blower accidentally inventing the microscope (like Leeuwenhoek in real history) than it is for a time traveler to try to build a microscope - the time traveler will be blinded by his high-tech thinking. Even in Leeuwenhoek's time, lens makers who've been making glass lenses for telescopes and spectacles for hundreds of years were blinded by their association of the word "lens" with grinding. $\endgroup$ – slebetman Mar 17 '15 at 18:43
  • $\begingroup$ this is actually quite interesting, and will help me when I get sent back in time. However, this still leaves the question as to what period a time traveler could create a microscope. This leaves two questions then. 1) could a time traveler and glass maker together be reasonable expected to come up with the non-grinding approach if they didn't know of it (sounds like the answer is no?) 2) when would the grinding approach be viable? $\endgroup$ – dsollen Mar 17 '15 at 18:57
  • $\begingroup$ I'm afraid I can't quite answer you there as it involves creativity more than technology. What Leeuwenhoek did was just one step above a little kid looking through a clear glass marble. Technology wise, it can be done when glass blowing gets invented. Creativity... well, Archimedes came up with an explanation for buoyancy long before Newton introduced maths to physics. Today to explain what Archimedes discovered we show schoolkids equations and force-vector diagrams. Archimedes didn't have the thinking tools we have today but still managed to get an "AHA" moment. $\endgroup$ – slebetman Mar 17 '15 at 21:09
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Well according to wikipedia, the first microscope was made between the 1200's and 1600, so actually the middle ages are not that far off. You can also look at this page http://en.wikipedia.org/wiki/Timeline_of_microscope_technology, which links to the book [*], which may probably answer all of your questions.

About the fact of finding germs, it is said once again on wikipedia that the first bacteria was found in the 1600s thanks to a "single-lens microscope". So I assume that as soon as you have a basic microscope and that you look in the right direction, you can actually find germs.

[*]: Bardell, D. 2004. “The Invention of the Microscope”.

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    $\begingroup$ There you go, quoting real life to answer my reality check questions. That's just blasphemy!! $\endgroup$ – dsollen Mar 17 '15 at 14:26
  • $\begingroup$ @dsollen The truth is stranger than fiction. $\endgroup$ – acbabis Mar 17 '15 at 17:53
  • $\begingroup$ This is a much more realistic answer. $\endgroup$ – RBarryYoung Mar 17 '15 at 20:29
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All you need is someone with the basic theory of lenses, and enough favor to get someone to help do the work.

Glass has been around since 4000 BC. So any time after that you could get someone to form you some glass disks, and then practice grinding and polishing to get the shapes. It would take some trial and error if you'd never done it before, but the hardest part is knowing which lens shapes to use. Even a rough idea, along with the knowledge it's possible, would give you hundreds of years of advantage.

So absolutely possible.

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    $\begingroup$ I know glass was around, I was less confident about the ability to refine it to make precise enough lenses that even stacked on top of each other they wouldn't distort an image to the degree that it couldn't be made out. $\endgroup$ – dsollen Mar 17 '15 at 14:28
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    $\begingroup$ @dsollen I think that's where the polishing would play a big role. Most of the glass back then was wavy because of how they formed it, so it would be pretty rough to begin with. The first glass containers were made by covering a sand form with molten glass. By polishing it you'd take off the surface irregularities while getting the correct shape. After that the biggest problem would be bubbles in the glass, but since you'd be working with fairly small pieces you could just have the glass maker keep making and remaking disks until you got enough good ones. $\endgroup$ – AndyD273 Mar 17 '15 at 14:38
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    $\begingroup$ "Any time after 4000 BC" is wildly misleading for a number of reasons. But to be succinct, what you really need is transparent, uncolored glass intentionally created of sufficiently high quality to be used for lenses. And so far this appears to have been first produced around 1200 AD. $\endgroup$ – RBarryYoung Mar 17 '15 at 20:27
  • $\begingroup$ @RBarryYoung does that mean that a microscope could be made as early as 1200? or are there other requirements, like better grinding ability or better understanding of ideal lens shape etc, which would require a greater delay? again assuming the time traveler can only give a basic idea of stacking lenses and has to leave it up to experts of that time to figure out the mechanics. $\endgroup$ – dsollen Mar 18 '15 at 15:22
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    $\begingroup$ quartz crystals can be very clear - one just needs to dig them up and polish them. That takes time, but could be done in the stone age as there is no technological requirement aside from knowledge of the optic principles behind lenses. $\endgroup$ – pluckedkiwi Mar 18 '15 at 20:54
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You can make a crude microscope by placing a drop of water on a slide to act as a lens. This brings the list of stuff he needed to have in his pocket down to a mirror (rescue signal mirror or makeup compact will work) two slides, and a slide cover. An eye dropper is also nice, but with practice you can use a finger to place a single drop of water.

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  • $\begingroup$ This is what I wanted to say. In school we learned that van Leeuwenhoek started out this way. $\endgroup$ – RedSonja Mar 18 '15 at 9:05

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