Interactive Primary Bulletin 38
Science is just magic!

Eye Eye Sir

Once light has passed through parts of the eye which are visible from the outside (cornea, lens and iris) it goes, funnily enough, through the watery insides (aqueous humour) and falls on the retina at the back. The retina has a thin layer of light-sensitive cells, some of which detect colour (cones) and others black and white (rods). Different cones, of which there are three, are sensitive to green, red or blue.

Figure 14 - Fish cards

If you look for a prolonged time at an image of one strong colour (say green), the green sensitive cells will tire. If you then switch your gaze to a white surface, which will be reflecting red, blue and green light, these tired cells will fail to respond to the green light, but the others will react strongly to the red and blue, and you will see a red-blue image.

Figure 15 - Fish bowl

Prepare cards as above, or use an interactive whiteboard to project images. Give your volunteer one coloured fish and tell them to stare at the fish’s eye. Ask them to switch their gaze to a card or whiteboard image of an empty bowl (Fig. 15). They should be able to see a ghostly fish in the reverse colour.

Good, good, good ... good vibrations