Cotsen Ghosties

book cover 3Last 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.

Seeing Spirits

seeing spiritsA 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 Pepper’s Ghost (invented by English scientist John Henry Pepper in 1862). We conjured it at To Be Continued, our chapter book story time program for 6-8 year-olds. Scroll to the bottom of the post to see a video of the illusion in action!

We read Arlo Finch in the Lake of the Moon, written by John August (Roaring Brook Press, 2019). Summer camp for most kids means bonfires, canoeing, and hiking. But for Arlo Finch and his friends, it means surviving the supernatural forces of the Long Woods. Doppelgangers, menacing strangers, talking foxes, locations both in and out of time, and a mysterious object unearthed after decades in hiding test both Arlo’s courage, and his friends’ loyalty.

In the book, Arlo has a special ability to see the spectral world. And I’ve wanted to make a Pepper’s Ghost project for kids for AGES. Through an afternoon of happy experimenting, I was able to construction this inexpensive and kid-friendly tabletop version.

You’ll need:

  • 2 large tissue boxes
  • A box cutter
  • 1 toilet paper tube
  • 1 piece of glass or clear polystyrene (more on this below)
  • White card stock
  • Scissors, glue, and tape for construction
  • Markers for decorating

First, cut the lids off the top of a pair of large tissue boxes. Then cut the boxes in such a way as to create an L shape box like so:

ghost box step 1The L shape box is consists of two sections: a “forest section” and a “ghost section.”

ghost box sectionsNext, 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.

ghost box step 2In 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.

ghost box step 3 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.

ghost box step 4Next, 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):

fox spiritTape 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.

ghost box step 5Now 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.

ghost box step 6During 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!

The final piece of the Pepper’s Ghost illusion is the lighting. First, cover the area above the view finder with a square of cardboard…

ghost box step 7Then 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.

ghost box step 8Ready 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!


This isn’t the first time the To Be Continued kids have adventured with Arlo Finch and his friends. We read the first book, Arlo Finch in the Valley of Fire earlier in the program (you can see the project we did here). The kids voted unanimously to read the sequel. It did not disappoint. The Arlo Finch books are full of action, intrigue, mystery, and humor. I highly recommend them!

O Frabjous Day

go ask aliceThis year marks the 150th anniversary of the publication of Alice in Wonderland, and we decided to honor the occasion at Princeton University’s Community & Staff Day! Our event table was stocked with some super, yet simple-to-assemble, thaumatropes. There was also some breakdancing. Well, sort of. Scroll to the bottom of the post to see our mashup of Alice and the 1980s.

A thaumatrope is a Victorian optical toy. It consists of two images printed on opposite sides of a paper disc or card. When you twirl the thaumatrope, its two pictures appear to blend into one. Most thaumatropes are twirled using string. We decided to mount ours on pencils.

thaumatrope demoYou’ll need:

  • 1 Alice thaumatrope template, printed on 8.5″ x 11″ white card stock
  • 1 pencil (I ordered terrific ones from Oriental Trading Company)
  • Scissors and tape for construction
  • Colored pencils (or crayons) for decorating

We offered 4 Alice-themed templates, drawn by our amazing student artist, Aliisa Lee.

thaumatropesFirst, select a template, and use colored pencils or crayons to color it. Then, fold the template in half (along its faint grey line).

folded thaumatropeFlip the thaumatrope over, and tape a pencil to the back of one of the panels like so:

thaumatrope step 2Fold the thaumatrope closed, then secure the panels together with a piece of tape. You’ll also want to tape both sides of the thaumatrope to the pencil, to make it extra sturdy.

thaumatrope step 3Hold the pencil between your palms and roll it briskly back and forth. Your thaumatrope will turn, and the two images will appear as one!

twirlingHere’s what our craft table looked like (and, if you’d like to explain a bit of the science behind how the device works, here’s a pdf of our thaumatrope table sign):

thaumatrope work tableWe also had some pens and blank thaumatrope cards on hand, just in case kids wanted to try their hands at making one from scratch.

blank thaumatropeOn the other side of our event tent, we loaded a table with optical illusions cards, tops, Photicular bookmarks, flip books, replicas of vintage thaumatropes, kaleidoscopes, and mini chess boards.

optical illusion tableWhile color print-outs of optical illusions work just fine, I highly recommend this pack of Usborne optical illusion cards. There are 50 illusions in the pack. They’re colorful, sturdy, and the science behind the illusions is explained on the back of the cards. The deck retails for $10.

optical illusion cardsNo event is complete without a little costuming, and Marissa and I raided both our closets and the Costume Shop at the Lewis Center for the Arts for our garb. This was completely unintentional when we snapped the shot, but…don’t Marissa and I look like we’re going to bust out some 80s breakdancing moves?

break danceMaybe it’s the shoes? The jaunty pose? Hmmmm. What if we adjust the backdrop a little…

welcome to the 80sOh yeah. I dare you to pin it.


Many thanks to the Costume Shop at the Lewis Center for the Arts for the costume loans, and to Aliisa Lee for triggering some totally radical 80s flashbacks.