GROOVED SURFACES OF METALLIC AND TRANSPARENT BODIES. 311 
Number of 
grooves in 
an inch. 
Maximum tint without a fluid. 
2000 Greenish yellow of second order 
2500 Blue, second order 
3333 Gamboge yellow of first order 
Maximum tint, with water, alcohol, and oil of cassia. 
IS. 
P- 
1 ?: 
n- 
13 . 
Water. Brownish red, second order. 
Alcohol. Pinkish red, ditto. 
Oil of cassia. Greenish blue. 
Water. Dilute green. 
Alcohol. Greenish white, second order. 
Oil of cassia. Bright gamboge yellow. 
Water. Pinkish red, first order. 
Alcohol. Reddish pink. 
Oil of cassia. Bright blue, second order. 
5000 Bluish white of second order 
IS. 
Water. Pale yellow. 
Alcohol. Yellow with tinge of orange. 
Oil of cassia. Yellowish pink, second order. 
P- Water. Greenish white of second order. 
10,000 Fine blue of second order <^ -2. Alcohol. Yellowish white. 
LS. 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 refractive 
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 ordinary 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 symme- 
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 
