THe shadow in the submarine photographs (previous post) float in the air because there is a parallax between the flashes of each photograph as well as the parallax between the two photographs. Instrument six has an object to cast shadows and a screen. For direct viewing there are two candles (see above) on a track that have a polarising filter for each candle. There is also a mechanism to adjust the distance between the candles. The screen is a material that maintains the polarisation of light in the reflection, and is made for 3D projection. The observer wears polarising glasses and the parallax between the two shadows locate a single shadow in front of the screen. By reversing the filters the shadow can be placed behind the screen.
When taking photographs a single clear light bulb is used on the same track. A left eye image is taken and then the camera shifted 65mm to the right for a series of right eye shots. For each of these the light is moved along the track progressively, so that when they are each combined with the left eye picture, they place the shadow at different depths.
To view the shadow in 3D go cross eyed so that the two shadows register one over the other. Try to relax and the 3D image will appear. You will see the shadow sitting a short distance off the surface of the screen. When viewing like this you will see three images with the 3D version in the middle. The lines on the screen are there to help resolve the 3D image and are not needed in the direct viewing version.