[ 13° ] 



through the glafs, v/ould either totally difappear, or become a faint 

 and diluted red. But, on e^|briment it appeared of a purple co- 

 lour. The purple in this cafe could not be a primitive and ori- 

 ginal colour, as is manifeft, becaufe it did not proceed from the 

 purple part of the fpedrum ; we muft therefore conclude, that it 

 was a compound colour. But purple, when compound, is made 

 up of blue and red, therefore it follows, that feme blue rays did 

 adually exift in the red part of the fpedrum ; which combined 

 with the few, ftraggling red rays which penetrated the blue glafs, 

 compofed that purple colour, which the red extremity of the 

 fpedrum affumed, when viewed by the light tranfmitted through 

 the blue medium. 



To try, on the other hand, whether any red rays lay hid amongft 

 the blue, I proceeded in the fame manner, and looking at the 

 blueft part of the fpedrum through a red glafs, it appeared of a 

 purple colour; Ibme red rays therefore are equally refrangible 

 with the blue ; and if the red extends as far as the blue, there is 

 no reafon why we may not fuppofe that it extends fomewhat far- 

 ther, fo as to compound, with a diluted blue, the extreme colours 

 of the fpedrum, indigo and violet. 



Bdt it may be faid, that if blue rays exifted amongft the red, 

 that part of the fpedrum could not appear fo extremely brilliant 

 as it really does; but would put on a purplifh appearance in the 

 fpedrum itfelf,.even to the naked eye. In anfwer to this objedion 



we 



