ON THE NATURE OF HEAT. ^55 



of these facts must necessarily proceed on some other prin* 



It is certain, that two ener^jetic, but opposite powers,. are Attraction ^ni 

 constantly active, in all the operations of chemistry; these '^^^^^^"''^ 

 are attraction and repulsion. The nature however of these 

 powers is still very uncertain : the effects of heat are all re- 

 ferrible to changes in their condition ; but from our igno- 

 rance of their nature, it must be extremely difficult, to 

 ascertain with precision the cause and nature of the changes 

 they undergo. 



The phenomena which I have mentioned as contradictory Accounted for 

 to the theory of repulsive caloric have been ascribed to the 7 ^^^"^ 

 agency of a certain polarity in the particles of the body ; by 

 means of this polarity the particles are opposed to each other 

 in a particular manner; and the state of attraction and re- 

 pulsion is influenced or regulated by this state of apposition. 

 The change in temperature is the cause of the change in the 

 apposition ot' the particles; and this change of apposition of 

 the particles proves the cause of the change in the state of 

 attraction and repulsion, and consequently of the bulk of 

 the body. 



This explanation is probably correct; and if it apply in Change of 

 one instance of changes produced by temperature, why not J^"^*^ ^'^<'™ 

 in all? The greatest density of water seems to be about 

 the temperature of 38**. If its temperature suffer any 

 change from this point, expansion occurs; and for any 

 given number of degrees above or below this temperature, 

 the expansion is the same, if the water retain the fluid 

 force. Here therefore, the effects are precisely similar, but, 

 according to the theory, they are ascribed to causes that are 

 different; which in itself appears to me contraiy to the true 

 laws of philosophising. This opinion, therefore, and the 

 objections which I have mentioned to the usual explanation, 

 have induced me to refer the changes of bulk from tempera- 

 ture, in every case, to the same cause; whatever the cause 

 may be. 



There are many circumstances, which tend to corroborate Circumstancet 

 the idea of polarity. The appearances of crystallization ap- h"ypoth"I[f^* 

 pear to depend on its agency. The state of fluidity of bodies polarity, 

 must also be referred to the ** particular situation" of their 



particles^ 



