SYMBOLS FOB DESIGNATING LIGHT. 29 



something which transmits the light. It is supposed that 

 one or the other of these two suppositions must be correct, 

 because these are the only two ways in which we can con- 

 ceive that action of any kind can be conveyed through 

 space. But whether there may not be modes of transmis- 

 sion for force that man, with his present mental constitu- 

 tion, can not conceive of, is a grave question. 



At any rate, it is now universally agreed among scien- 

 tific men to regard light as transmitted by a series of un- 

 dulatory movements in an intervening medium, and all 

 the calculations and all the language used in describing 

 the phenomena are based at the present day on this hy- 

 pothesis. In all the drawings, however, and other illustra- 

 tions intended to represent the action of light to the eye, 

 the radiation is represented by lines, which are more ap- 

 propriate to the idea of a progressive motion of streams 

 of particles than to that of undulations. We are obliged 

 to use both these modes, as the best symbols of thought 

 at our command ; but when we attempt to pass from these 

 symbols to the realities which they are intended to repre- 

 sent, we are lost in wondering what the actual nature of 

 emanations can be that can thus meet, and cross, and en- 

 counter each other in every imaginable way in such 

 countless numbers, within such inconceivably narrow lim- 

 its, and at such inconceivably rapid rates of motion and 

 each of the millions of separate motions pursue its own 

 way without being in the least degree deranged, disturbed, 

 or interfered with by the rest. We ask ourselves in amaze- 

 ment, What can the emanation be, in its intrinsic nature, 

 that can exist under such conditions as these? What is 

 light ? We can not tell. We can really know nothing of 

 its essential nature. We can only study such of its modes 

 of action and such of its effects as come within the reach 

 of our senses and of our half-developed reasoning powers. 



