320 



HEAT. 



the parent and the nurse of the endless beauties of organization. The mine- 

 ral, the vegetable, the animal kingdoms, are its offspring. Erery natural strue- 

 ture is either immediately produced by its agency, maintained by its influence, 

 or intimately dependant on it. Withdraw heat, and instantly all life, motie, 

 form, and beauty, will cease to exist, and it may be literally said, " Chats has 

 come again." 



Nor is heat less instrumental in the processes of art, than in the operations 

 of nature. All that art can effect on the productions of nature is to chaage 

 their form or arrangement to separate or to combine them. Bodies are moulded 

 to forms which our wants or our tastes demand ; compounds are decomposed, 

 and their obnoxious or useless elements expelled, in obedience to our wiihos. 

 In all such processes heat is the agent. At its bidding the most obdurate masses 

 soften like wax, and are fashioned to suit our most wayward caprices. Ele- 

 ments of bodies knit together by the most stubborn affinities by forces which 

 might well be deemed invincible are torn asunder by this omnipotent solvent, 

 and separately presented for the uc 3 or the pleasure of man, the great Master 

 of Art. 



If we turn from art to science, we find heat assisting or obstructing, as the 

 case may be, but always modifying the objects of our inquiry. The common 

 spectator, who, on a clear night, beholds the firmament, thinks he obtains a just 

 notion of the position and arrangement of the brilliant objects with which it is 

 so richly furnished. The more exact vision of the astronomer discovers, how- 

 ever, that he beholds this starry vault through a distorting medium ; that, in 

 fact, he views it through a great lens of air, by which every object is removed 

 from its proper place ; nay, more, that this distortion varies from night to night, 

 and from hour to hour varies with the varying heat of the atmosphere which 

 produces it. Such distortion, and the variations to which it is subject, must 

 then be accurately sustained, before any inferences can be made respecting the 

 motion, position, magnitude, or distance of any object in the heavens ; and as- 

 certained it cannot be, unless the laws that govern the phenomena of heat be 

 known. 



But the very instruments which the same astronomer uses to assist his vis- 

 ion, and to note and measure the positions and mutual distances of the objects 

 of his inquiry, are themselves eminently subject to the same distorting influence. 

 The metal of which they are formed swells and contracts with every fluctuation 

 in the heat to which it is exposed. A sunbeam, a blast of cold air nay, the 

 very heat of the astronomer's own body must produce effects on the figure of 

 the brazen arch by whose divided surface his measurements and his observations 

 are effected. Such effects must therefore be known, and taken into account, 

 ere he can hope to attain that accuracy which the delicacy of his investigations 

 renders indispensably necessary. 



The chemist, in all his proceedings, is beset with the effects of heat, aiding 

 or impeding his researches. Now it promotes the disunion of combined ele- 

 ments, now fuses into one uniform mass the most heterogeneous materials. 

 At one time he resorts to it as the means of arousing dormant affinities ; at an- 

 other he applies its powers to dissolve the strongest bonds of chemical attrac- 

 tion. Composition and decomposition are equally attended by its evolution and 

 absorption ; and often to such an extent as to produce tremendous explosions 

 on the one hand, or cold, exceeding the rigors of the most severe polar winter, 

 on the other. 



But why repair to the observatory of the astronomer or to the laboratory of 

 the chemist, for examples of a principle which is in never-ceasing operation 

 around us ! Sleeping or waking, at home or abroad, by night or by day, at 

 rest or in motion, in the country or in the town, traversing the burning limits of 



