Mr. Morgan's Obfervdtions and Experhnents, &c. lot 

 efcape fooner than others. Thofe which are united with theleafl 

 degree of power will efcape firll, and thofe which adhere to it 

 mod ftrongly will (if I may be allowed the expre(hon) be the 

 lall: to quit their bafis. We may here have recourfe to a flimiliar 

 fa6l, which is analogous to this, and will illuflrate it. 

 If a mixture, confifting of equal parts of water, of fpirits 

 of wine, and of other more fixed bodies, be placed over 

 a fire ; the firft influence of that heat, to which all the in- 

 gredients ar€ alike expofed, will carry off the fpirits of 

 wine only. The next will carry off the fpirits of wine 

 blended with particles of water. A flill greater degree of 

 heat will blend with the vapour which efcapes a part of 

 the more fixed bodies, till at length what evaporates will be a 

 mixture of all the ingredients which were at firft expofed to 

 the fire. In like manner, when the furface of a combuflible is 

 in aflate of decompofition, thofe parts which are the leafl fixed, 

 or which are united to it with the leafl force, will be feparated 

 firfl. Amongft thefe the indigo rays of light will make the 

 earliefl: appearance. By increafing the heat we fhall mix the 

 violet with the indigo. By increafing it flill more we fhall add 

 the blue and the green to the mixture, till at length we reach 

 that intenfity of heat which will caufe all the rays to efcape 

 at the fame inflant, and make the flame of a combuflible 

 perfedlly white. It is not my pre fen t defign to fhew why 

 the mofl refrangible rays are the firfl which efcape from a 

 burning body, but to enumerate the feveral fads which feem to 

 fhew, that fuch a general law takes place in combuftion ; and 

 that the various colours of bodies in this flate are uniformly 

 regulated by that decreafe of attradive force now defcribed. 



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