AND THE THEORY OF LIGHT. 91 



by gradations of light and shade, the pulsations of light 

 being repeated at greater intervals than science teaches, 

 and do not depend on rays having different degrees of 

 refrangibiUty , nor on rays or waves, some of which are 

 repeated in a given time more frequently than others. 



141. These experiments, taken in cumulo, show us light 

 in two different states, in an increasing and in a decreas- 

 ing state. To the former belong red and its allies, orange 

 and yellow ; to the latter blue and its allies. 



The sensations produced by these two states of the 

 ether may appear astonishing to some because they are 

 novel, and make what were formerly only ideas or concep- 

 tions of the mind appear, as it were, palpable to the senses. 

 For everything which is seen is considered to be palpable 

 or material. But on due reflection they are not more 

 wonderful than other operations of nature. Who would 

 anticipate that heat and cold are but modifications of 

 one law ? For we say that the sensation of heat arises 

 from an increasing or absorbing operation; that of cold 

 from a decreasing or radiating operation. We even speak 

 of colours as warm and cold. We call red and its alHes 

 warm, blue and its allies cold. Green is warm when it 

 partakes largely of yellow, cold when blue predominates ; 

 the colours arranging themselves, according to our sensa- 

 tions, under the law which we have discovered. 



But we must lay speculation aside for the present. The 

 metaphysics of every operation ends ultimately in the 

 unconditioned ; the final cause merges in the infinite. 



142. At this stage of our inquiry there naturally arises 

 an extremely interesting question, viz : How does nature 

 produce these penumbrse, this gradation of light and shade 

 of which we have been speaking? To enter into all the 

 minutiae, and to attempt an explanation of the whole 

 circle of optical phenomena, would be impossible ; every 

 one must apply the principles of the science for himself. 



