GROOVED SURFACES OF METALLIC AND TRANSPARENT BODIES. 305 
Scarlet. 
Purple. 
Third limit of pink and blue . 
Blue. 
48 00 
Brilliant green. 
Yellowish green. 
Yellow. 
Reddish .... 
10 00 
Such being the phenomena exhibited by the ordinary image formed by re- 
flexion from the original spaces n, I now proceeded to examine the prismatic 
images in the first specimen with 1000 grooves, and I observed the following 
appearances. 
Let A B, Fig. 1 , be the reflected image 
of the rectangular aperture from the spaces 
n, and a b, a' V , a" b", a" 1 V", the prismatic 
images of it, v v, v' v', &c. being the violet 
sides, and rr^r 1 r', &c. the red sides of these 
spectra. Then in the 
1st spectrum a b, the violet rays are ob- 
literated at m at an incidence of 74°, and 
the red rays at n at an incidence of 66°, 
the intermediate colours, blue green, being 
obliterated at intermediate points between 
m and n, and at angles of incidence inter- 
mediate between 74° and 66°. In the 
2nd spectrum a! b', the violet rays are 
obliterated at m! at an incidence of 66° 20', 
and the red at ri at 55° 45'. In the 
3rd spectrum a” b”, the violet rays are 
obliterated at m" at 5 7°, and the red at w" 
at 41° 35'. And in the 
4th spectrum a'" b'", the violet rays are 
obliterated at m'" at 48°, and the red rays at n'" at 23° 30'. 
Another similar succession of obliterated tints takes place on all the pris- 
matic images at a lesser incidence, as shown at ^ v, v', the violet being obli- 
terated at (jb , and the red at v, and the intermediate colours at intermediate 
2 R 
MDCCCXXIX. 
