Guide students to visualize the analogy described in the text: boats are only rocked by waves of a size (have a wavelength) that is in proportion to the size of boat. Certain cells in the retina of the eye (cone cells) have molecules that are only “rocked” by certain wavelengths. The “rocking” of these molecules causes them to send impulses to the brain which interprets them colors as described in the following video. (Have students note that electromagnetic waves have no color as such. It is our brains receiving impulses from these different receptors that gives us the perception of color.: