GROOVED SURFACES OF METALLIC AND TRANSPARENT BODIES. 



303 



»i + ra = lOOOdth of an inch, no less than four complete orders of colours 

 were developed as shown in the following Table. 



White 



Yellow 



Reddish orange 



Pink 



Junction of pink and blue 



Brilliant blue 



Whitish 



Yellow 



Pink 



Junction of pink and blue 

 Blue 



Bluish green 54 30 



Yellowish green 53 15 



Whitish green uigj).:.. 



Whitish yellow 49 



Yellow 47 15 



Pinkish yellow 41 



Pink red 36 



Whitish pink 31 



Green 24 



Yellow 10 



Reddish 



These colours are obviously those of the reflected rings in thin plates. By 

 turning the steel plate round in azimuth, the very same colours are seen at the 

 same angles of incidence, and they suffer no change either by varying the 

 distance of the luminous aperture, or the distance of the eye of the obsei-ver. 



I now examined various other specimens which possessed the same property. 

 In some there were three orders of colours, in others two, and others one, 

 while in some only one or two tints of the first order were developed. These 

 different effects are more minutely detailed in the following Table. 



Number of grooves 

 in an inch. 



Orders and portions of orders of colours developed from 

 90° up to 0° of incidence. 



500 Citron yellow of the first order. 



625 One complete order, and up to reddish yellow of the second order. 



Colours very dilute. 

 1000 Four complete orders of colours. 

 1000 One complete order, together with blue green and yellowish green of 



the second order. 

 1250 One complete order, together with blue and bluish green of the second 



order. Colours exceedingly faint and diluted. 

 2000 One complete order, together with blue green and greenish yellow of 



the second order. 



