GROOVED SURFACES OF METALLIC AND TRANSPARENT BODIES. 309 



Pink. 



2nd junction of pink and 



blue 57 40 



Bluish green. 



Yellow. 



Orange, 



Pink. 



3rd junction of pink and blue. 



First minimum of red 76 



Second 61 



The following results were obtained with Realgar 







pj^en4n9bi' 



White 90 



Yellow 80 



Pink 75 30 



1st junction of pink and 



blue 73 10 



Blue 72 



Bluish green 70 15 



First minimum of red , 

 Second 



Yellow . 63 



Bright pink 54 



2nd junction of pink and blue 47 



Bluish green 41 



Yellow 36 



Pink 32 



More and more pink. 



72 



61 15 



The following results were obtained with Isinglass. The colours were ge- 

 nerally the same as iii the steel. 



The first limit of pink and blue was at 75 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. 



