make others see. Our optics are none of the best, but we have seen the professor run down his ethereal game, and can attest that it was more exciting than a horse-race. Let us consider this "descent of man" into the regions of infinitesimal time.
Of all the curious things that science has revealed, none are so confounding to the ordinary reason as what has been learned respecting the order of Nature in its extremest aspect of minuteness. Objects fade away from the customary range of the senses, and we habitually think, what was long believed to be the fact, that there remains nothing more; or, that we find the edge and final termination of things but little beyond what is familiarly recognized. But we now understand that Nature is fathomless below as well as boundless above, and that, beneath the grasp of unaided sense, there are an inexhaustible wealth of wonders, a fixedness of relations, a definite play of interacting forces, and a sharp exactness in the working of law, which we could never infer from the coarser processes of the world of common experience.
As we are to speak of the briefest known duration of luminous effects, it will be proper first to recall how much is involved in the act of sight. When the man of experiment talks to us about what occurs in the thousandth of a second, he is, of course, dealing with something recognized, or which has affected both his body and his mind in that short space of time, and this is necessarily an illustration of how quickly his composite machinery can work. Then the agency which acts upon him must be taken into account, and also the cause of that agency, for they both belong to the same order of activities. When we look upon a source of illumination, as a candle or a star, we are affected by something that is done at those points. The light originates in the vibration of the molecules of matter. These vibrations are communicated to some medium which can convey the impulses at a demonstrated velocity of nearly 200,000 miles per second. The luminous waves strike the retina of the eye, and they are again translated into the molecular vibrations of nervous matter, and the physical influence is turned into a sensation by the organ of consciousness. The act of seeing thus involves the constitution and action of the visible object, the mode of movement of the force, the operation of the organ of vision, the changes of the nerve-line, and the cerebral act of recognition. There is a dynamic chain connecting thought and the object seen through a nether world of minuteness, but where all is correlated in a common scale of relations; and, whenever we see any thing, this whole train of transformations is implicated in the effect. The molecular tremors of Sirius, the ethereal thrills of space, and the rhythmic swing of the nervous elements, are but parts of a unified system of subsensible dynamics. Bearing in mind, then, what is involved in a single act of vision, let us now trace the course of experiment which has led to the latest results regarding its duration.