C 137 1 



centre of the re4 circle ; and if the number of red rays be to the 

 fum of the yellow and blue fays inverfely as the diftances of the 

 centre of the red circle, and the common centre of the yellow and 

 blue from the centre of the principal circle, the common centre of 

 gravity of the red, blue and yellow circles will coincide with the 

 centre of the principal circle, and therefore the nefulting compound 

 will be white. 



But it is manifefl that this conftrudlion cannot be relied on, 

 becaufe the quantities of the rays of any given colour in folar 

 light, do not appear to be proportional to the fpaces which they 

 occupy in the redilineal fides of the fpedrum. Thus it is known 

 that the yellow making rays are predominant in folar light, yet 

 the fpace they occupy in the fpedrum is to the fpace occupied ei- 

 ther by green or blue as four to five, and to the fpace occupied 

 by the violet only as three to five- 



Vol. VII.. 



