Scientists with creative imaginations are ever confronted by two opposing forces. One tempts them to soar into the realm of fancy, and the other cautions them to keep their feet on the ground. These conflicting influences play a significant part in the search for fundamental truth.

The complementary value of philosophical reasoning and matter-of-fact experimentation in the complete fulfillment of science is illustrated by many an epochal discovery. Von Laue had the brilliant thought that the symmetrical distribution of atoms in a crystal presents a lattice sufficiently fine to scatter the exceedingly small waves of X-rays. The idea appeared to be scientifically sound, at least to von Laue, but to certain of his colleagues, classicists all, it was untenable. The kinetic energy or heat-movement of the atoms would, they said, disturb the diffraction phenomena and obscure the picture. Von Laue had confidence in his hypothesis and the courage to see it through, but he also knew that the validity of a scientific theory lies in experimental verification. There were in his laboratory two assistants, both able experimenters, and they proved the truth of von Laue's dream.