2/2 Dr. Herschei/s Experiments for investigating 
side ; and by which, in the present case, the red part of the 
prismatic spectrum, that is, the red, orange, yellow, and some 
of the green, can only reach the eye. 
4S- Of a sudden Change of the Colours of the Bozvs. 
it has been shown that the red bow should be seen nearly 
in the same place where the Newtonian blue bow is visible. 
For in the 41st article the place of the eye, for seeing the blue 
bow in the prism of 100 degrees, was determined to be at an 
obliquity of 49 0 57' 3", 3 ; and with the red bow, and in the 
same prism, it has been shown that the eye must be placed at 
the obliquity of 49 0 38' 19", 5. The difference is only 18' 43", 8, 
and by the following experiments it will be found, that both 
the bows may actually be seen nearly in the same part of every 
prism ; and that the direction of the light, by which we see 
either the blue or the red bow, determines which of the two 
will be visible. To prove this, let a right angled prism be 
laid down on a sheet of white paper before a window, and 
when the eye is placed in the proper situation for seeing a re- 
flected blue bow, we may instantly transform it into a trans- 
mitted red one, by covering the side of the prism which is 
towards the incident light with a slip of pasteboard ; for by 
stopping the direct light, which before fell on the base of the 
prism, and was there reflected, we then see the bow by light 
intromitted from the paper through the base, which, as has 
been explained, will be red. 
With proper management we may have the bow half red 
and half blue ; blue in the middle with red sides, or red in 
the middle with blue sides ; which appearances it will not be 
required to explain any farther, especially after what has 
