274 Dr. Herschei/s Experiments for investigating 
prism instead of a right angled one. When the reflecting 
paper is removed from the wall and laid under the prism, that 
the light may then be thrown upwards and transmitted through 
the base, we see a bow of a lively red colour. 
Before I can introduce more intricate phenomena, it will be 
necessary to advert to some other particulars relating to these 
bows. 
44. Of Streaks and other Phenomena produced from the prismatic 
blue and red Bows. 
It has been remarked in the 40th article, that the production 
of colours and their configuration when produced are owing 
to different causes ; this will now be confirmed by an experi- 
ment. 
Scattered rays, when they fall on a prism will by a critical 
separation of the colours, produce both the blue and the red 
bows, and these coloured appearances when produced may be 
modified into streaks, circular rings, and other forms, by the 
configurating power of surfaces. When a plain glass or me- 
talline mirror is laid under the base of a right angled prism in 
which we see the blue bow, the contact of the two plain surfaces 
will immediately produce a great number of coloured streaks. 
They will be found to be parallel to the bow, most of them within 
and some just under it. They may be seen without any lens, 
merely by looking into the prism with the eye pretty close to 
the surface through which we see the blue bow. This expe- 
riment proves that plain surfaces, though they cannot produce 
colours, have a power of modifying and multiplying them 
when produced. As I shall have occasion hereafter to be more 
particular, I shall now only mention that when we lay a 
