light at the surfcices of different media. 



221 



Image at the Surface of Prism A. 



Oil of Fenugreek. — Colours rather bet- 

 ter than the preceding. Heat brings 

 out three good orders. First Umit 

 at 75°. 



Oil of Caraway-seeds. — Two orders, not 

 good. 



Oil of Thyme. — Slight tinges of colour. 

 Heat brings out two good orders. 



Oil of Turpentine. — Two tolerably good 

 orders. First limit at 74°. 



Cajeput Oil. — Two tolerably good or- 

 ders. First red bad, second red good. 



Linseed Oil. — Two extremely faint or- 

 ders. Three good orders brought 

 out by heat. First limit at 73°. 



Train Oil. — Three very good orders. 

 First red and first blue excellent. 

 First limit at 73°. Heat spoils the 

 first order. 



Oil of Savine. — Almost no colours, both 

 images being yellowish, and that of 

 B brightest. Heat brings out three 

 orders. First limit at 80°, which a 

 greater heat brings to 75°. 



Oil of Pennyroyal. — Almost no colours. 

 A sort of bluish gray when cold. Heat 

 brings out two good orders when temp, 

 only 90°, but greater heat injures 

 them. 



Oil of Almonds. — Three tolerable or- 

 ders. First red bad, second red good. 



Oil of Mace. — Gives three and a quar- 

 ter orders when cold. First limit 

 at about 80°. 



When the film of the oil begins to 

 crystallize, it displays red, blue, and 

 |L, greenish tints, at the same incidence, 

 ■k^ in different places. 



Image at the 

 Surface of Prism B. 



Whitish yellow. 



Whitish yellow. 

 Yellowish white. 

 Whitish yellow. 

 Yellowish white. 



Yellowish white. 



Yellowish white. 



Yellowish white. 



Yellowish white. 



Yellowish white. 



Pretty bright. 



