GROOVED SURFACES OF METALLIC AND TRANSPARENT BODIES. 309 
Pink. 
2nd junction of pink and 
blue 57 40 
Bluish green. 
First minimum of red 
Second 
Yellow. 
Orange. 
Pink. 
3rd junction of pink and blue. 
76 
61 
The following results were obtained with Realgar. 
White 
O 
90 
/ 
0 
Yellow 
0 
63 
Yellow 
80 
Bright pink 
54 
Pink . 
75 
30 
2nd junction of pink and blue 
47 
1st junction of pink and 
Bluish green 
41 
blue 
73 
10 
Yellow 
36 
Blue 
72 
Pink 
32 
Bluish green 
70 
15 
More and more pink. 
. • 0 f 
First minimum of red 72 0 
Second 61 15 
. • 0 f 
First minimum of red 72 0 
Second 61 15 
The following results were obtained with Isinglass. The colours were ge- 
nerally the same as in the steel. 
0 ' 
The first limit of pink and blue was at . . . . . . 76 45 
The blue of second order 73 45 
The second limit of pink and blue was at 54 30 
In these experiments the tin gave nearly the same results as the steel ; but 
in the realgar and the isinglass similar tints were produced at a less angle of 
incidence than in the steel. The minima of the periods were exhibited very 
finely on the isinglass, and were produced at smaller angles of incidence. 
In a specimen with 1000 grooves upon isinglass, the third pink, or that seen 
upon steel at 36°, was the highest ; but after drying, the pink descended to 
yellow, and subsequently to green. 
If the isinglass is removed from the steel when it is still soft, the edges of 
the grooves get rounded and lose their sharpness, and only one prismatic 
image is seen on each side of the ordinary image, as in mother-of-pearl. 
