394 BACON 



The difference of which we now speak is common also to the 

 nature of cold, in which the contracting motion is restrained by 

 the resistance of expansion, as in heat the expansive motion is 

 restrained by the resistance of contraction. 



Whether, therefore, the particles of matter penetrate inwards 

 or outwards, the reasoning is the same, though the power be 

 very different, because we have nothing on earth which is in- 

 tensely cold. 



IV. The fourth difference is a modification of the preceding, 

 namely, that this stimulating or penetrating motion should be 

 rapid and never sluggish, and should take place not in the very 

 minutest particles, but rather in those of some tolerable dimen- 

 sions. 



It is shown by comparing the effects of fire with those of time. 

 Time dries, consumes, undermines, and reduces to ashes as well 

 as fire, and perhaps to a much finer degree ; but as its motion is 

 very slow, and attacks very minute particles, no heat is per- 

 ceived. 



It is also shown in a comparison of the dissolution of iron and 

 gold ; for gold is dissolved without the excitement of any heat, 

 but iron with a vehement excitement of it, although most in the 

 same time, because in the former the penetration of the sepa- 

 rating acid is mild, and gently insinuates itself, and the particles 

 of gold yield easily, but the penetration of iron is violent, and 

 attended with some struggle, and its particles are more ob- 

 stinate. 



It is partially shown, also, in some gangrenes and mortifica- 

 tions of flesh, which do not excite great heat or pain, from the 

 gentle nature of the putrefaction. 



Let this suffice for a first vintage, or the commencement of 

 the interpretation of the form of heat by the liberty of the un- 

 derstanding. 



From this first vintage the form or true definition of heat 

 (considered relatively to the universe and not to the sense) is 

 briefly thus: Heat is an expansive motion restrained, and 

 striving to exert itself in the smaller particles. The expansion is 

 modified by its tendency to rise, though expanding towards 

 the exterior ; and the effort is modified by its not being slug- 

 gish, but active and somewhat violent. 



With regard to the operative definition, the matter is the 

 same. If you are able to excite a dilating or expansive motion 

 in any natural body, and so to repress that motion and force it 

 on itself as not to allow the expansion to proceed equally, but 

 only to be partially exerted and partially repressed, you will be- 

 yond all doubt produce heat, without any consideration as to 

 whether the body be of earth (or elementary, as they term it), 

 or imbued with celestial influence, luminous or opaque, rare or 



