272 Colours of opake Bodies. [Book III. 



was of different colours. The fame fluids, fpread 

 thinly on a white ground, exhibited their proper co- 

 lours -, the light indeed being in this cafe reflected from 

 the white ground, and tranfmitted through a coloured 

 medium. It is almofl unnecefiary to add, that when 

 fpread upon a black ground they afforded no co- 

 lour. 



The fame experiments were repeated with glafs 

 tinged of various colours, and the refult was perfectly 

 the fame. When thefe glaffes are of fuch a thinnefs, 

 and are tinged fo dilutely that light is tranfmitted 

 through them, they appear vividly coloured; when in 

 larger maffes, and the tinging matter more denfely dif- 

 fufed through them, they are black ; when the tranf- 

 mitted light, in the tranfparent plates of thefe glafll j s, 

 was intercepted by covering the further furface, they 

 appeared black. 



From thefe different phenomena Mr. Delaval clearly 

 deduces thefe remarks ift, That the colouring par- 

 ticles do not reflect any light, adly, That a medium, 

 fuch as Sirlfaac Newton has defcribed, is diffufed over 

 the anterior and further furfaces of the plates, where- 

 by objects are reflected equally and regularly as in a 

 mirror. 



When a lighted candle is placed near one of thefe 

 coloured plates, the flame is reflected by the medium 

 diffufed over the anterior furface j the image thus re- 

 fie&ed refemb'es the flame in fize and colour ; for it is 

 fcarcely fenfibly diminifhed, and is not at all tinged 

 with colours : if the plate is not very maffy, or too 

 deeply tinged, there appears a lecondary image of the 

 flame, reflected from the further furface of the glafs, 

 and as the light, thus reflected, pafles back through the 

 coloured glafs, it is vividly tinged. 



The fecondary image is ids than that which is re- 

 flected 



