56 Dr Brewster on a new series of 



^"•°^ Maximum tint 



grooves Without a fluid Maximum tint, with water, alcohol, and oil of cassia. 



Jl. Water. Tinge of Yellow. 

 2. Alcohol. Tinge of Yellow. 

 >r 1 3- Oil of cassia. Faint reddish yellow. 



500 Citron yellow f^' Y,^^f'\ ^}\'ff/'^\ 

 of first order, if ^If^^/^* Diluted pmk. 



i3. Oil or cassia. A bluer pink. 



625 Reddish vellow, C^' ^^^^^^ Faint pink of second order, 

 of second'order J Alcohol. Ditto more pink. 



' ^3. Oil of cassia. Bluish pink, of second order. 



1000 Yellowish green H' Y^^X'\ Pinkish red, second order. 



^n^ , ^, < 2. Alcohol. Brilhant pink, ditto. 



of second order, ^3 gji ^^^.^^ g^^J;^,, i,,^^_ ,j 



third order. 



loftA Tii^joi. «,«^« fl- Water. Yellow of second order. 



feim 1^- ^^^«^^«^- Yellower. 



' ( 3. Oil of cassia. Yellowish pink, 



onn.k r>^^^^: -u 1^ C i- Water. Brownish red, second order. 

 ^fTnn^^^'^^ 2. Alcohol. Pinkish red, ditto, 

 of second order. 1 3^ oil of cassia. Greenish blue. 



2500 Blue, second il' Y,^X'\ ^^^^^^^ P^^^^"; ., , , 



order i Alcohol. Greenish white, second order. 



' (3. Oil of cassia. Bright gamboge yellow. 



'^ * (3. Oil of cassia. Bright blue, second order. 



5000 Bluish white of V' ^:'''^\ Pale yellow 



second order 1 ^' ^^^^^^^- Yellow with tinge of orange. 



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



irtrkArt j?-^ ui V fl' Water. Greenish white of second order. 



fprJlrdpr •< 2. Alcohol. Yellowish white, 



second order, ^^ ^ ^.^ ^^ ^^^^.^^ Brilliant gamboge yellow. 



I obtained similar results with grooves impressed upon wax ; 

 so that we may now safely draw the conclusion that more or- 

 ders of colours, and consequently higher tints at a given in- 

 cidence, are developed by diminishing the refractive power of 

 the grooved surface. 



The influence of refractive power on the tints of the ordi- 

 nary image being thus determined, it became interesting to as- 

 certain its efi^ects on the obliterated tints of the prismatic ima- 

 ges. 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 maxi- 

 mum tint a blue of the second order, but which exhibited no 

 obliterated tints in the prismatic images. Having placed upon 



