HEAT. 



'*$*> TO""*/'" 



'UNIVERSITY 



CHAPTER I. 



General Remarks, upon the Agency of 

 Heat, and its connexion with Chemi- 

 cal Science. 



IN all our excursions over the surface of 

 this globe, innumerable objects excite 

 our admiration, and contribute to in- 

 spire delight. But whether our grati- 

 tude is awakened by the verdure of the 

 earth, the lustre of the waters, or the 

 freshness of the air, it is to the benefi- 

 cial agency of Heat (under Providence) 

 that we are indebted for them all. 

 Without the presence and effects of 

 heat, the earth would be an impenetrable 

 rock, incapable of supporting animal or 

 vegetable life ; the waters would be for 

 ever deprived of their fluidity and mo- 

 tion ; and the air of its elasticity and its 

 utility together. 



Heat animates, invigorates, and beau- 

 tifies all nature. Its influence is abso- 

 lutely necessary to enable plants to grow, 

 put forth their flowers, and perfect their 

 fruit. It is closely connected with the 

 powers of life ; since animated beings 

 lose their vitality when heat is withdrawn. 

 Such is the universal influence of this 

 powerful agent in the kingdoms of na- 

 ture ; nor is this influence diminished in 

 the provinces of art. It is with the aid of 

 heat that rocks are rent, and the hidden 

 -treasures of the earth obtained. Matter 

 is modified ten thousand ways by its 

 agency, and rendered subservient to the 

 uses of man ; furnishing him with 

 useful and appropriate instruments, 

 warm and ornamental clothing:, whole- 

 some and delicious food, neeciful and 

 effectual shelter. 



Increase of temperature facilitates the 

 operations of chemistry in various ways ; 

 but chiefly by heightening the attrac- 

 tive forces which the particles of mat- 

 ter exert for each other, and thus ena- 

 bling them to combine together. In 

 many instances the particles which enter 

 into the composition of compound bo- 

 dies may remain in close contact with- 

 out uniting, unless the temperature is 

 raised, and then the combination pro- 

 ceeds with rapidity. 

 The term Caloric was introduced by 



Lavoisier to distinguish the cause of 

 heat from the sensation which we call 

 by the same name ; but the terms caloric 

 and calorific fluid seem to imply the ma- 

 terial nature of heat, which has not yet 

 been proved. The heat of the sun's rays 

 is a common form of expression; it 

 seems to convey just as clear an idea as 

 the caloric of the sun's rays ; and is 

 more conformable to common modes of 

 speech : the heat which we feel is ano- 

 ther equally common form of expression, 

 which applies to the sensation produced, 

 while the former use of the word marks 

 the cause, whatever it be, that produces 

 the sensation. The common usage 

 has long been, it thus appears, to apply 

 this term both to heat, and to the 

 sensation which heat produces ; and it 

 is still so applied in the works of the 

 most scientific writers ; the meaning of 

 the expression in which it is used being 

 considered sufficient to prevent any am- 

 biguity or confusion. The author of 

 this treatise does not, therefore, consider 

 himself bound to adhere to the term 

 caloric, although he may sometimes find 

 the use of it convenient. 



CHAPTER II. 

 Of the Nature or Cause of Heat. 



WHOEVER is employed in examining 

 refined and powerful natural agencies, 

 must speedily be convinced that the 

 causes of such agencies still continue 

 unknown; notwithstanding the patient 

 and persevering efforts of learned men, 

 through many ages of investigation. 

 This is strictly true with regard to heat 

 or caloric ; concerning which it cannot 

 be determined whether its phenomena 

 are occasioned by a subtile fluid, capa- 

 ble of entering into bodies and of being 

 emitted from them, or by motion, vibra- 

 tion, or rotation excited among the parti- 

 cles of matter. The arguments which 

 have been adduced, and the experi- 

 ments which have been made, are incon- 

 clusive, however varied and ingenious 

 they may be. 



Pictet suspended a thermometer in an 

 exhausted receiver ; and, finding that it 

 \vas capable of undergoing changes of 



