MEMOIR V.] INTERFERENCE OF RADIATIONS. 93 



monochromatic rays were used along with daylight, 

 Herschel having previously shown in similar experi- 

 ments that new phenomena arise during the conjoint ac- 

 tion of rays (PM. Trans., 1840, 64). The following 

 are some of the observations I made; their date is Sept. 

 24, 1842. 



The red ray when projected increases the length of 

 the solarized portion, and also of its white extremities. 



The yellow ray shortens the solarized portion. 



The green ray exerts a greater action of the same kind. 



The indigo ray gives a most remarkable result. It to- 

 tally inverts the action of the less refrangible rays, and 

 they solarize the plate, acting in the same way that the 

 more refrangible rays commonly do, causing it to exhibit 

 a watch-spring lustre. 



I further found that when different rays are brought 

 to act upon each other, the result does not alone depend 

 upon their intrinsic differences, but also on their relative 

 intensities. Thus the green and lower half of the blue 

 rays, when of a certain intensity, protect the plate from 

 the action of the daylight ; but if of a less intensity, they 

 aid the daylight. 



The red and orange rays, when of a certain intensity, 

 increase the action of daylight on the plate ; but if of a 

 less intensity, they restrain it. 



These facts seem to be connected with the circum- 

 stance that there is often to be traced on daguerreotype 

 plates a remarkable difference between the central and 

 lateral parts of a spectrum. Thus if a line be drawn 

 through the centre of such a spectrum and a parallel to 

 it on one of the edges, the action at any point on the cen- 

 tral line is the reverse of that at the corresponding point 

 on the edge. A similar remark, as respects impressions 

 on paper, has been previously made by Herschel. 



Such are the chief facts I have observed in relation to 



