Permanent Colours of Opake Bodies. 2 \ 7 



that, every fmall mafs of air, or of the rarer 

 medium, which fills the pores, or interdices, 

 of denfe bodies, is a minute white fubftance. 



This is m.anifefl", in the whitenefs of froth, 

 and of all pellucid Colourlefs Bodies, fuch as 

 glafs, cryflal, or falts, reduced to powder, or 

 otherwife flawed. For, in all thefe inflances, 

 a White Light is rejected from the air, or rarer 

 medium, which intercede the particles of the 

 denfer fubftances, whofe interftices they occupy. 



All pellucid Colourlefs Subftances become 

 opake and white, by the admixture of pellucid 

 colourlefs media of confiderably different den- 

 fnies : as in the inftanees which have been here- 

 adduced. And all Opake White Subflances 

 are rendered pellucid and colourlefs, by reducino- 

 them to uniform malTes, whofe component pans 

 are, every where, of nearly the fame denfity. 

 Becaufe, all reflexions are made at the furfaces 

 of bodies difi^cring, in denfity, from the ambient 

 medium ; and, in the confines of equally denfe 

 media, there is no reflection. 



Thus, opake white earths are reducible to 

 Pellucid Colourlefs Glafltrs, by proper fluxes, 

 and a fufficient degree of hear. When the 

 particles of air and water, united in the fmall 

 bubbles of which white froth confifls, are fepa- 

 rated from one another, each of them conftitutes 

 Sn uniform. Pellucid, Colourlefs Subflancc. 



AVhca 



