or waking, happily dreaming, or wrenched with pain, whether they have noticed it or not, the finger of this light has pointed towards them. When they were building the pyramids, five thousand years ago, straight the arrow of light shot from the sun, lit their dusky forms, and glowed on the endless sand. Endless as that desert sand may be, innumerable in multitude its grains, there was and is a ray of light for each. A ray for every invisible atom that dances in the air--for the million million changing facets of the million ocean waves. Immense as these numbers may be, they are not incomprehensible. The priestess at Delphi in her moment of inspiration declared that she knew the number of the sands. Such number falls into insignificance before the mere thought of light, its speed, its quantity, its existence over space, and yet the idea of light is easy to the mind. The mind is the priestess of the Delphic temple of our bodies, and sees and understands things for which language is imperfect, and notation deficient. There is a secret alphabet in it to every letter of which we unconsciously assign a value, just as the mathematician may represent a thousand by the letter A. In my own mind the idea of light is associated with the colour yellow, not the yellow of the painters, or of flowers, but a quick flash. This quick bright flash of palest yellow in the thousandth of an instant reminds me, or rather conveys in itself, the whole idea of light--the accumulated idea of study and thought. I suppose it to be a memory of looking at the sun--a quick glance at the sun leaves something such an impression on the retina. With that physical impression all the calculations that I have read, and all the ideas that have occurred to me, are bound up. It is the sign--the letter--the expression of light. To the builders of the pyramids came the arrow from the sun, tinting their dusky forms, and glowing in the sand. To me it comes white and spectral in the silence, a finger pointed, a voice saying, 'Even now you know nothing.' Five thousand years since they were fully persuaded that they understood the universe, the course of the stars, and the secrets of life and death. What did they know of the beam of light that shone on the sonorous lap of their statue Memnon? The telescope, the microscope, and the prism have parted light and divided it, till it seems as if further discovery were impossible. This beam of light brings an account of the sun, clear as if written in actual letters, for example stating that certain minerals are as certainly there as they are here. But when in the silence I see the pale visitant at my bedside, and the mind rushes in one spring back to the builders of the pyramids who were equally sure with us, the thought will come to me that even now there may be messages in that beam undeciphered. With a turn of the heliograph, a mere turn of the wrist, a message is easily flashed twenty miles to the observer.