Permanent Colours of Opake Bodies. 25 1 ^ 



caufe v/hich is here confidered, excepting fuch 

 jis relate to yellow liquors, which are apt to 

 tranfmit orange, and red colours, in proportion 

 as the rays are tranfmitted through greater 

 thicknefles of fuch media. 



Sir Ifaac Newton, in the following pafTage, has 

 attributed, to red liquors, the property of tranf- 

 jnitting thefe colours, according to the dif- 

 ferent thicknefies of the liquors. *' A red liquor 

 " in a conical glafs held between the light and 

 " the eye, looks of a pale and dilute yellow at 

 ^* the bottom where it is thin, and a little higher 

 ^' where it is thicker grov/s orange, and where 

 ^' it is ftill thicker becomes red, and where it is 

 *' the thickefl: the red is deepeft and darkeft." * 



The liquor, which was the fubjecl of this 

 obfervation, was, probably, an aqueous or 

 fpirituous infufion of fome of the woods which 

 are ufed in dying red. For, thefe tranfmit a 

 yellow, orange, or red colour, according to their 

 thicknedes, or tenuity. 



But, red liquors do not tranfmit orange, or 

 yellow, colours, even when fpread thin. Several 

 red liquors are enumerated in the table p. i66, 

 fuch as the nitrous folution of cobalt, the red 

 infufions of flov/erS;, the red juices of fruits, and 

 berries ; and fevcral others. When thefe liquors 

 ^re difpofed in thicker, or thinner, mafles, they 



^ Newton. Opt. L. I. Part. IF. Prop. X, Probl. V. 



do 



