An Entroposcope is described in his second book, "Lost in a Good Book" as a jam jar containing an equal volume of rice and lentils. By shaking the device, you can measure ambient levels of entropy. If they mix in a normal clumping pattern, entropy is normal. If they begin to separate, you should be on the lookout for highly unlikely events to occurr.
The jar was made using 3 6 inch round lemon cake layers (with raspberry filling between), each cut in half (one baked in a countour pan for the top and bottom) and a 4 inch layer for the lid. The cake was iced with yellow buttercream. Rice was made of white chocolate, and the lentils were chocolate chips. The lid was painted with gold lustre dust, and the jar coated with a neutral fruit glaze to give it a glass-like sheen. The label was an edible image.
I was pleased with the cake, and Jasper and Mari appeared to be as well.
Photos taken by and copyright Twila Davis Reed.