Ok forget I said frosted. I still think it’s only purpose is as a spacer for storage.
a polarizer?
What kind of school, and what department?
It vaguely reminds me of an opaque overhead projector; the kind that can throw an image onto a screen of an object on the desk, without the object needing to be transparent.
I encountered those when I was in high school, 37-41 years ago.
This is high school science. The school is only 25 years old. We have had various weird donations over the years from various enthusiasts trying to enliven the science department. We recently acquired a SPEC20, which I remember from university days which I am sure we will never use.
Is it dividing the views in two? If so, looks like it’s for adjusting two light sources to the same brightness or color. An intensity comparator (using human eyes to judge when the line between them disappears.)
If so, it might be part of an “inverse squared” physics demo. You’d have two frosted bulbs in boxes shining out through 1" square holes. Start with each bulb facing one of the two “input” windows, and placed equal distances to the comparison box, then use a dimmer to set them to exactly equal brightness.
Next cover all but 1/4 of one frosted bulb’s square window, then move that one inwards until again they’re at the same brightness in the comparison box. You should have moved that 25%-bright source in to 1/2 of its original distance. (Or cover the source by 1/2, and you have to move it to 0.707 of it’s original distance: sqrt(2) )
If I’m right, then you should look for two similar boxes with light bulbs inside, and the same metal rods sticking out.
Heh. I remember working on SPEC20s back in the '90s. In case you ever do use it, and you lose signal strength, here’s a protip: Make sure that the bulb that comprises the light source is installed so that the filament is parallel to the cuvette.
Save you a trip to the shop. 
If its a sample compartment or intended to hold anything inside its a very dumb design. The lid needs to be unscrewed which is not convenient. Also, with the wax slabs removed the glass windows fall into the compartment. There is nothing holding them in their frames.
If you shine two light bulbs into the two side-holes, can you move the bulbs closer and farther until the image becomes uniform? (until there is no obvious line between the two glowing halves?)
If so, then the wax is a light diffuser, and the device provides a simple way to adjust two sources until they have the same brightness.
I wonder if it might be one of those devices used in photography to transfer negatives to photographic paper. You would put the developed negatives in the device then adjust the height to get the image on the paper. I think the arm is pretty clearly there as part of a support system that can be adjusted for height. Then you expose your photo paper and develop the image.
Someone with experience in photography will know what I mean. It probably has a name. Is there a dark room anywhere in the building?
It’s called an ‘enlarger’ - Enlarger - Wikipedia .
I suspect wbeaty has it.
It is a classroom demonstrator for the inverse square law. The spike goes into a holder, the square opening faces the class, and the round openings face to each side. You use a set of identical light sources either side of the device. Put one source on each side and you find that the luminosities balance when they are equidistant. Two one side, one the other, you need to move them about until the distance ratio is root two, then three to one, needs root three, four to one, needs root four = two, and so on.
My father likes to relate how he did the experiment in the 1930’s with a piece of paper with a grease spot on it, and a set of candles. This device seems to be directed at demonstrating the experiment to an audience rather than for individual students to use.
I still don’t know why an optical device has wax blocks in it.
They’re optical diffusers.
Probably the original inventor lived in the early 1900s where household wax blocks for jam jars was a common product and “opal glass” was not. If you wanted to build a large number of these for sale to cash-strapped teachers, wax makes it easy to do.
That does not sound reasonable to me. Frosted glass has been around for a lot longer than that.
They are a 3D diffuser. Opal glass is only a 2D diffuser. The blocks are viewed from 90 degrees from where the light enters. There should be a separating sheet between the blocks.
Anyway, a quick bit of searching reveals that this is indeed what the device is - its proper name is a Joly Photometer. It is used to demonstrate the inverse square law of light.
Good info. I looked and found that John Joly (1857 – 1933) was sure an interesting scientist. He worked on radio dating of minerals and the earth, radiotherapy for cancer, plants, thermodynamics and photography. He was at the end of the time when people with the right stuff could have wide impact in many sciences.
Photo slide viewer?
Not projector, viewer.
Or, filmstrip tech. In a school, that would made sense.
Any dates inscribed on it?