4j6 Mr. Delaval on the Caufe of the 



appears from feveral parts of this inquiry, that 

 Tranfparent Coloured Liquors do not refled 

 any colour, but appear black when viewed by 

 incident light : therefore, the atoiofphere, which 

 exhibits colours by reflcding the incident light, 

 does not, in its optical properties, refemble 

 fuch liquors. 



Mr. Melvill not only acquiefces in the general 

 opinion, that colours are produced by the re- 

 fieftion of the feveral rays, from the Colouring 

 Particles: but he extends his do?:rine of the 

 refleiftive power of thofe particles, fo far as to 

 attribute to them the aftion on light, whereby 

 opake bodies are fooner heated by the fun-beams, 

 than tranfparent ones. " As (according to him) 

 *' each cclorific particle of an opake body, by the 

 " readion of the particles of light, muft be 

 *' fomewhat moved, when the light is refleSled 

 ** backward and forward between the fame 

 " particles, it is manifelt, that they likewife mufl: 

 " be driven backward and forward with a vibra- 



*' tory motion." * 



With refpeift to this hypothefis, I (hall only 

 obferve, that, as the Colouring Particles of bodies 

 do not refledt the rays, but appear black by 

 incident light, even when contiguous to air ; 

 they cannot, according to any optical law, exer- 

 cife a refleftive power, when they are in contadl 

 with the internal parts of media, whofe denfity 



* lb. p. 20. 



greatly 



