Termanent Colours of Opake Bodies. ay i 



of the fcience of optics, and of the arts which are 

 dependent upon it. This experimental refearch 

 was undertaken, for the purpofe of examining 

 the optical qualities of fuch fubftances. 



During the courfe of my inquiry, I have ob- 

 ferved, that the tranfition from phyfical experi- 

 ments, to practical operations of dying, is eafy 

 and obvious. For, tlie experiments, which I have 

 made, with a view of invcftigating the origin and 

 caufe of colours, have guided me to the difcovery 

 of feveral bright and permanent dyes, in the exe- 

 cution of which I have, principally, ufed cheap 

 and common ingredients, that have not before 

 been applied to fuch purpofes. 



I do not doubt, that a clear, and comprehenfive, 

 view of the principles of the art will open, to the 

 artifts who pradife it, a fertile fource, from which, 

 with certainty and facility, they may derive the 

 difcovery of new materials, and of the mofl ad- 

 vantageous means of employing them. 



The art of painting, alfo, will receive great ad- 

 vantage, from an accurate and precife conception 

 of the principles, by means of which the colouring 

 matters, endued with a refle(fl:ive power, may be 

 diflinguifhed from others which tranfmit the rays> 

 but do not rcfledl them. 



The works of many painters greatly excel in 

 the clearnefs and brightnefs of their colouring:* 



but 



• Several of the greateft mailers praftifed a method of 

 colouring, which was, in fome refpefts, conformable to 



the 



