Last Halloween season we took a stroll through our special collections pumpkin patch. Today, we’re looking for ghosts! And we found them in this amazing optical illusion book titled Spectropia; or, Surprising Spectral Illusions. Showing ghosts everywhere, and of any color. Published by J.H. Brown in London in 1864, the book teaches the concept of “the persistency of impressions, and the production of complementary colours on, the retina.”
The illusion is very simple. In the image above, stare at the small black dot by the ghost’s neck for 20-30 seconds. Then look away at a white wall or ceiling. Her ghostly image will appear in your vision, except in different colors (in this case green wreath, blue ghost)!
Scientifically speaking, this is called an afterimage. The color receptors in your eyes work in pairs (red/green, blue/yellow, etc.). When you stare at the drawing and one color fatigues your receptors, the other receptor will step in and dominate for a bit.
The book has a very lengthy description of this concept, as well as viewing instructions that include having the “gaslight turned low.”
Spectropia also has a disclaimer at the beginning: “As an apology for the apparent disregard of taste and fine art in the plates, such figures are selected as best serve the purpose for which they are intended.”
I wish they might have reprinted the disclaimer before THIS image, which honestly is going to haunt me clear through December:
The book concludes with a grand finale image that is not a ghost, but a rainbow! Definitely try this one, because it is so cool to see the colors flip in the afterimage!
Looking more more optical spooky fun? Try making our tabletop Pepper’s Ghost illusion!
Images from Spectropia; or, Surprising Spectral Illusions. Showing ghosts everywhere, and of any color. J.H. Brown, London. Griffith and Farran.1864. Cotsen Children’s Library, Department of Special Collections, Princeton University Library.
A quiet forest appears empty. But gaze long enough and…a fox spirit will magically appear before your eyes! No, its not Photoshop or camera trickery. It’s a simple physical stage illusion called 
The L shape box is consists of two sections: a “forest section” and a “ghost section.”
Next, cut a small square (approximately 1.75″ x 1.75″) in the side of the box that faces the forest section. This is your viewfinder.
In the book, Arlo gazes through a slipknot, a loop of rope or lacing that allows him to see and travel multidimensionally. In order to replicate that rounded view, we slid a 2.25″ piece of toilet paper tube into the viewfinder as well.
Now draw a backdrop for the wall opposite the viewfinder. I had the kids decorate a pre-cut piece of paper or cardboard, then we glued it to the inside of the box.
Next, sketch a ghost on a piece of white card stock. Here’s my tribute to Fox, a spirit from the book (and my favorite character):
Tape the ghost in the ghost section of the Pepper’s Ghost box. Though you will probably need to do a little adjusting on the exact placement, try to arrange the ghost in the center of the section. I found this gave the best results.
Now for the magic! A Pepper’s Ghost illusion is essentially a reflection. For this model, the reflection is caused by a piece of glass or clear polystyrene set at a 45 degree angle in the junction of the L shaped box.
During my initial test, I used a piece of glass from a 4″ x 6″ picture frame. However, I was a little uncomfortable giving multiple 6-8 year-old kids pieces of glass to take home. Luckily, I found clear polystyrene sheets on Amazon (a set of ten, 8″ x 10″ sheets cost $15). Polystyrene is plastic, lighter weight, doesn’t shatter, and you can cut it down to size with a box cutter or scissors. Testing revealed that the reflection illusion works just as well with polystyrene as glass. Yay!
Then hinge a second square of cardboard over the ghost section. It’s important that this flap open and close. With the flap closed, the ghost will not appear through the viewfinder. But when you lift the flap, the ghost section will illuminate, causing a reflection to appear.
Ready to see the illusion in action? Close the flap and peer through the viewfinder. Keep gazing through the viewfinder, then lift the flap over the ghost section. Your ghost will magically appear! I also encouraged kids to stick their hands in the forest section and try to grab the ghost. Their fingers passed right through it, of course!
