“Moonlight,” I replied, “is, of course, reflected sunlight. But the rays which pass back to Earth after their impact on the moon’s surface are profoundly changed. The spectroscope shows that they lose practically all the slower vibrations we call red and infrared, while the extremely rapid vibrations we call the violet and ultraviolet are accelerated and altered. Many scientists hold that there is an unknown element in the moon⁠—perhaps that which makes the gigantic luminous trails that radiate in all directions from the lunar crater Tycho⁠—whose energies are absorbed by and carried on the moon rays.

“At any rate, whether by the loss of the vibrations of the red or by the addition of this mysterious force, the light of the moon becomes something entirely different from mere modified sunlight⁠—just as the addition or subtraction of one other chemical in a compound of several makes the product a substance with entirely different energies and potentialities.