GROOVED SURFACES OF METALLIC AND TRANSPARENT BODIES. 311 



grooves in Maximum tint without a fluid. Maximiun tint, with water, alcohol, and oil of cassia, 



an inch. Tl. Water. Brownish red, second Order. 



2000 Greenish yellow of second order ... . <^ 2. Alcohol. Pinkish red, ditto. 



Oil of cassia. Greenish blue. 



{i; 

 (1: 



(1: 



Water. Dilute green. 



2d00 Blue, second order -^2. Alcohol. Greenish white, second order. 



Ofl of cassia. Bright gamboge yellow. 



Water. Pinkish red, first order. 



3333 Gamboge yellow of first order •^2. Alcohol. Reddish pink. 



.3. Oil of cassia. Bright blue, second order. 



Water. Pale yellow. 



5000 Bluish white of second order «^ 2. Alcohol. Yellow with tinge of orange. 



,3. Oil of cassia. Yellowish pink, second order. 



Water. Greenish white of second order. 



10,000 Fine blue of second order -^2. Alcohol. Yellowish white. 



Oil of cassia. Brilliant gamboge yellow. 



I obtained similar results with grooves impressed upon wax ; so that we may 

 now safely draw the conclusion that more orders of colours, and consequently 

 higher tints at a given incidence, are developed by diminishing the i-efractive 

 power of the grooved surface. 



The influence of refractive power on the tints of the ordinary image being 

 thus determined, it became interesting to ascertain its effects on the obliterated 

 tints of the prismatic images. As these tints never appeared unless when 

 that of the ordinai-y image exceeded the blue of the second order, I took the 

 specimen with 10,000 grooves, which had for its maximum tint a blue of the 

 second order, but which exhibited no obliterated tints in the prismatic images. 

 Having placed upon it a film of oil of cassia, I raised the blue to a gamboge 

 yellow, and I found that the fluid developed the phenomena of obliterated tints 

 on the first prismatic image. Owing to the great breadth of the spectrum, the 

 distinct separation of the colours which composed it, and the great length of 

 the line of obliteration, this phenomenon was one of the most beautiful and 

 remarkable that I have ever witnessed. 



Hitherto I had examined the minima in the prismatic images as symmer 

 trically related in position to the minima in the ordinary image, as shown in 

 Figs. 1 and 2 ; but in studying some specimens in which the spaces n were 

 very broad, and the grooves or spaces m comparatively narrow, I was sur- 

 prised to observe obliterated tints on the prismatic images, while the ordinary 



