Here is the answer to the last "What the Heck Is This?" question. In short, the answer is a "Polarization Apparatus". And who is the winner? This round goes to Pieter Kuiper. Here is his answer.
Impressive answer. I have to admit that I was pretty confused when I first found this device. But then I looked in our Tome of All Things (and ancient CENCO catalog) and found this:
Awesome? Indeed. I love this thing. So, how does it work? First, once you realize that this thing is old, you might realize that we didn't always have polarizing sheets of material. If you wanted polarized light, you had to make the old fashioned way - reflect it.
Polarized Light
What is polarized light? Maybe the most visual way to think of this to consider a string. If you shake the string up and down, you will send a wave down that string.
Of course, you could shake the end up and down or side to side or diagonally to diagonally (but not Diagon Alley). What if you had a whole bunch of strings and you shake made waves on them in all different directions at the same time. If you looked at these strings head on, it would look something like this.
This would be a good representation for unpolarized light. If you were able to restrict the oscillations in the strings to just one direction, it would look like this:
Boom. Polarized string waves. They are all oscillating in the same direction. Now remember, this is just an analogy. Really, for light there other types of polarization, but I think you get the idea.
Polarization by Reflection
When light hits a material with a different index of refraction, some light goes through the material and some light is reflected off the material. The reflected light can be polarized (depending on the angle of incidence).
At a certain angle, all of the reflected light is polarized. This is called Brewster's angle (not to be confused with Brewster's Millions). Brewster's angle depends on the index of refraction of the two materials.
For light going from air (index of refraction around 1.0) to glass (about 1.5), Brewster's angle would be around 34°.
Why Not Just Use Polarized Filters?
Each end of the device has a piece of glass mounted to reflect light. If the light reflects, it would be polarized (if at Brewster's angle). But here is the cool part. Polaroid (the company) created the first polarizer in 1929. Before that, this device was basically your only option for polarized light.
How Does This Work?
As I mentioned in the first post, I am missing a piece of this device. There should be an arm to mount some type of light source that can be rotated. Let me make a diagram to show how this would work (top view).
No, I don't think that helps. I am trying to show that light comes in and reflects off the first glass (the one on the right). At the correct incident angle this would be polarized. Next the light reflects off the second glass (on the left). If this second plate is rotated so that the light would reflect up, the plane of polarization would be 90 degrees to the initial reflection. So, no light would be reflected. You can achieve the same thing by rotating two polarizers in a line. When you light passes through the first one, it becomes polarized. If the axis of polarization for the second polarizer is turned 90 degrees with respect to the first one, no light will get through.
Since my diagram wasn't the best, here is a video showing the apparatus (again, not the best video).
So, that is it. I am not sure what experiment you were supposed to do with this apparatus. I could be used as a demonstration, but how would you measure the variation in the intensity of light? Well, I have an idea but it would be a pain in the rear to do.
An Actual Experiment
One of the things I like to do with this old equipment is to redo the experiment with a modern twist. My idea was to use a laser pointer to reflect off the first glass and then the second. I would then measure the intensity of the laser reflection as a function of the second glass plate angle. There is one big problem with this plan: most laser pointers are already polarized. Yeah, I was surprised too. I think I could have still done the experiment, but I thought I would use that light instead. I just couldn't get it to work.
I actually did another experiment before using the angled glasses. I wanted to plot the intensity of light going through two polarizers as a function of angle. Here is the set up I made.
The basic idea is to get a plot of intensity vs. angle. The Vernier rotation sensor is my new favorite tool. The only problem is that in this setup the radius of the polarizer is different than the radius of the wheel on the sensor. This means the angle the sensor reads will be different than the angle of the rotated polarizer. So, the first step was to make this plot.
From the slope of this line, I can get the following conversion:
And here is the intensity vs. polarizer angle data.
The intensity doesn't go to zero since light could still get to the sensor through reflections with the walls and stuff.
I think I could still do the same thing with the two rotating glasses, but it is tricky to get it all lined up.
Conclusion: This post was way longer than it needed to be. I should have said "Pieter is the winner. It is a polarization apparatus."
