*Tarquin* Brielle is a very restful companion. We stroll to the bottom of the garden, where there is a little bench. Brielle is as fascinated by the composition of light in terms of waves and particles as I am. It is a real pleasure to talk the question through. I don’t even notice that it has grown a bit chilly until I inadvertently touch her arm and find it icy. “Miss Brielle, you seem to be very cold. We should return to the house.” She ignores me. “I wonder whether it would influence the experiment if you slanted the paper that you are using to split the light into rainbows.” “What do you mean?” “Well, if I understood you correctly, you are holding a card with a vertical slit up to the window.” I nod. “As the light strikes the slit, it divides into a rainbow, thereby demonstrati

