Mr, Morgan’s Ohfervations and Experiments, &c. 19 f 
efcape fooner than others. Thofe which are united with theleaft 
degree of power will efcape firft, and thofe which adhere to it 
mo ft ftrongly will (if I may be allowed the exprefiion) be the 
lafl: to quit their balls. We may here have recourfe to a familiar 
fa (ft, which is analogous to this, and will illuftrate 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 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 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 combuftible is ; 
In a ftate of decompofition, thofe parts which are the ieaft fixed, 
or which are united to it with the leaft 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 ftill 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 inftant, and make the flame of a combuftible 
perfectly white. It is not my prefent defign to fhew why 
the moft refrangible rays are the firft which efcape from a 
burning body, but to enumerate the feveral faffs which feem to 3 
fhew, that fuch a general law takes place in combuftion ; and 
that the various colours of bodies in this ftate are uniformly 
a 
regulated by that decreafe of attra&ive force now deferibed. 
