Mr, Mo'RGAi^^s Ohfervatlous and Experiments^ &c. 191 



efcdpefooner than others. Thofe which are united with theleaft 

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

 moft ftrongly will (if I may be allov/ed the expreflion) be the 

 lall; to quit their bafis. We may here have recourfe to a familiar 

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

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

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

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

 gredients are 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 ftill greater degree of 

 heat will blend w4th the vapour which efcapes a part of 

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

 mixture of all the ingredients which were at fird expofed to 

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

 inaftate of decompofition, thofe parts which are the lead: fixed, 

 or which are united to it with the leaf!: force,, will be feparated 

 firft. Amongft thefe the indigo rays of light will make the- 

 earlieft appearance. By increafing the heat we fhall mix the' 

 violet with the indigo. By increafing it dill more we diall 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 indant, and make the flame of a combudible 

 perfectly white. It is not tny prefent deiign to fhew why 

 the mod: refrangible rays are the fird which efcape from a 

 burning body, but to enumerate the feveral hSis which feemtd^ 

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

 that the various colours of bodies in this date are uniforixily 

 regulated by that decreafe of attractive force now defcribed. " 



