3 io THE POPULAR SCIENCE MONTHLY. 



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 respect- 

 ing the order of Nature in its extremest aspect of minuteness. Ob- 

 jects fade away from the customary range of the senses, and we habit- 

 ually 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 under- 

 stand 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 interact- 

 ing 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 quick- 

 ly 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 origi- 

 nates 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 trans- 

 lated into the molecular vibrations of nervous matter, and the physi- 

 cal influence is turned into a sensation by the organ of consciousness. 

 The act of seeing thus involves the constitution and action of the visi- 

 ble 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 sys- 

 tem of subsensible dynamics. Bearing in mind, then, what is in- 

 volved in a single act of vision, let us now trace the course of experi- 

 ment which has led to the latest results regarding its duration. 



