(H-O-H, H-O-H) circuit diagrams used in electronics; optical drawings showing the paths of light rays; plates showing tracks of subatomic particles; and the 'trees' used by linguists to represent structures or sentences.
Einstein's theory of general relativity explained how it is possible for mass and energy to be interconvertible, and for light rays to be curved even in a vacuum. Other possibilities explained before specimens were produced include lasers and super-conductivity. Some of the theories listed so far not only explained possibilities, but also contained enough detail to make prediction, and in some cases control, possible. This is fairly common in physics, though more difficult in biology. In the case of the human sciences (and philosophy) the ability to predict and Page 28 control is rare.