1 1 2 Mr. Delaval on the Caufe of the 



the fame manner as thofe of the fpecimens which 

 I have here defcribed. 



In all chcfe inftances, the colours of the bodies 

 are produced by the light refleded from a white 

 fubftance, and tranfmitted back from thence, 

 through a tranfparent coloured covering. The 

 colouring particles have been extra(fled from fuch 

 of the bodies, as were capable of yielding them 

 to any proper fol vents : and in their Hate of fo- 

 lution, as well as when condenfed into ,a folid 

 confiftence, they have been conftancly found to 

 pofiefs a power of tranfmitting colour, but to be 

 devoid of any refleflive power. 



In the examination of fome animal fubjedls, 

 when the colouring matter could not be feparated 

 from the white fubftance, by chemical means, I 

 have had recourfe to mechanical methods of cf- 

 feding their divifion. But, fuch methods can 

 only be employed, when the principal part of 

 the white fubftance is unmixed with the coloured 

 coat or covering, which is fpread upon its furface. 

 The mineral kingdom affords a great variety 

 of coloured fubftances. Thefe confift principally 

 of earthy, and metallic matters. 



The earths have been ufually arranged in three 

 clafTes, the filiceous, the calcareous, and the ar- 

 gillaceous, which is obtained pureft in the earth 

 of alum. To thefe, mineralogifts have lately 

 added rragnefia, and terra ponderofa, which is 

 the bafis of fpar. All thefe earths are perfcdly 



whitCi 



