GROOVED SURFACES OF METALLIC 
AND TRANSPARENT 
BODIES. 313 
Reflected tints. 
Transmitted tints. 
Angles of incidence. 
Yellow ......... 
Deep blue . . . 
. 90 
Orange 
Paler blue. 
Pink 
Blue. 
First limit of pink and blue . . 
Blue. 
Blue 
Pink. 
Green 
Orange pink. 
Yellow 
Orange. 
Orange 
Yellow. 
Pink 
Yellow. 
Second limit of pink and blue . 
Yellow. 
Blue 
Yellow . . . . 
. 0 
The comparison of these tints affords the most satisfactory evidence that they 
are not complementary to each other. The transmitted tints of the ordinary 
prismatic images always increase in brightness as the angle of incidence di- 
minishes, while the reflected tints become fainter. 
As I had preserved the different specimens of isinglass with which these ex- 
periments were made, it became interesting to observe the changes which their 
colours had undergone after a lapse of six years. The following was the 
result. 
1. A specimen with 1000 grooves exhibited no colours on the ordinary image 
either by reflexion or transmission. The prismatic images of a candle were 
very faint, and the 4th could scarcely be seen. 
2. Another specimen of 1000 grooves gave by reflexion one period of colours 
from white at great incidences through yellow up to purple at a vertical in- 
cidence. By transmission a little yellow only was seen at a great incidence. 
3. A third specimen of 1000 grooves which had been a fine sharp impression, 
gave by reflexion two orders of colours, the first limit of pink and blue being 
at 57° 45', and the second limit nearly at a vertical incidence, a deep pink 
appearing at 10°. By transmission the isinglass gave a bluish green at the 
greatest incidence which passed at lesser incidences through purple to yellow, 
which was the maximum tint. 
In all these specimens the colours remain the same in all azimuths, provided 
the angle of incidence is invariable. 
2 s 
MDCCCXXIX. 
