The mirascope! It’s a miracle! It’s a scope! Wait…is it really? Well, “miracle” derives from the Latin word miraculum meaning “object of wonder,” and “scope” comes from the Greek word skopein "to look": so it’s a miraculous object that involves sight, which seems like a pretty good word for this intriguing device.
The mirascope has an interesting history: a janitor discovered it accidentally in the closet of a college physics department! In the 1960s, Caliste Landry was cleaning a stack of large World War II surplus searchlight mirrors in a closet at the University of California Santa Barbara. Two of the mirrors were stacked atop each other, with a large hole on top (where the bulb for the searchlight originally went). Landry tried to wipe off some dust, and realized that the grime he was trying to clean wasn’t really there! He talked about it with one of the professors in the department, Virgil Elings, and in 1970 the two filed a patent on a device to replicate the effect: your mirascope.
In the simplest sense, as you can probably guess, the way the mirascope produces the illusory 3D image can be explained by the “law of reflection”: the angle of reflection of a ray of light is equal to the angle of incidence (the angle at which it comes in) compared to the surface where it strikes the mirror. Because the mirrors of the mirascope are parabolic, the angle for every ray of light is different than the one right next to it, and eventually they converge at a focal point. What’s interesting about the mirascope, and what makes it work, is that because the mirrors reflect into each other, each ray of light bounces not once but twice – first to the top mirror, then to the bottom mirror, then out the hole and into your eye!
When you place your tiny Inq (or anything else) in the mirascope, you actually get to see something incredible: two separate types of reflected images, known as a “real image” and a “virtual image.” The real image is what the mirascope is known for and what most people look at: the 3D reproduction of the original object, hanging in midair at the opening. If you look carefully, you’ll see the virtual image right below that: it looks like the original object upside down, attached right to the bottom of the “main” illusory Inq. A real image is one that optically speaking, really exists, with the image floating in space at the focal point where the reflecting light rays intersect at the opening. Here’s a fun trick: if you’ve got a laser pointer, you can shine it at the real image, and the light from the laser will scatter, just as if you were pointing at the real object.
Things get really funky with the upside-down, virtual image. A virtual image is one that is not really at the focal point, but appears to be so because of how light reflects in a mirror. For example, when you look at yourself in a regular flat mirror, optically what you’re seeing is classed as a virtual image of yourself – it looks like you, standing a few feet behind the mirror, which of course can’t be true because the mirror is attached to a wall. The amazing thing about the virtual image in the mirascope is this: because of the complex series of reflections occurring inside the device, the virtual image isn’t a reflection of the original object, but of the bottom of the real image (and whatever is on your ceiling). So you’re seeing a reflection of something that isn’t really there!
Isaac Newton wrote his classic book Optiks in 1704; the mirascope is a fun and fascinating reminder that even some of the oldest and most familiar concepts in science can still excite us in new and wondrous ways.