LIB. II. 20. 191 



transitiva, per quam corpus admotum corpori calido 

 incalescit, confundi debet cum forma calidi 29 . Aliud 

 enim est calidum, aliud calefactivum. Nam per mo- 

 tum attritionis inducitur calor absque aliquo calido 

 proecedente, unde excluditur calefactivum a forma ca 

 lidi. Atque etiam ubi calidum efficitur per approxi- 

 mationem calidi, hoc ipsum non fit ex forma calidi ; 

 sed omnino pendet a natura altiore et magis communi ; 

 viz. ex natura assimilationis sive multiplicationis sui : 

 de qua facienda est separatim inquisitio. 



At notio ignis plebeia est, et nihil valet : composita 

 enim est ex concursu qui fit calidi et lucidi in aliquo 

 corpore ; ut in flamma communi, et corporibus accensis 

 usque ad ruborem. 



Remoto itaque omni sequivoco, veniendum jam tan 

 dem est ad differentials veras, qua? limitant motum, et 

 constituunt eum in formam calidi. 



Prima igitur differentia ea est, quod calor sit motus 

 expansivus 30 , per quern corpus nititur ad dilatatio- 

 nem sui, et recipiendum se in majorem sphaeram sive 

 dimensionem, quam prius occupaverat. Hsec autem 

 differentia maxime ostenditur in flamma ; ubi fumus 

 sive halitus pinguis manifesto dilatatur et aperit se 

 in flammam. 



Ostenditur etiam in omni liquore fervente, qui 



29 Right. Cf. Herschel s Dis- the IVth Table (cf. supr. II. 18. Inst. 

 course, 345. The communication 10); nor does the distinction of 

 of Heat, (which results from the &quot; secundum totum&quot; throw much 

 Law of Heat, whereby it always light on it. See Limitation 3. The 

 endeavours to cause an equilibrium fact however is correct. The dila- 

 of temperature) is entirely distinct tation of bodies by Heat forms the 

 from Heat itself. subject of that separate branch of 



30 It would seem hard to recon- Science which is termed Pyrome- 

 cile this with the loth Rejection in try. 



