32 



CALORIC. 



perceive that the form of bodies is dependant on 

 heat. By its increase soHds are converted into li- 

 quids, and liquids are dissipated in vapour; by its 

 decrease vapours are condensed into liquids, and 

 these become solid. If matter ceased to be under 

 the influence of heat, all liquids, vapours, and, doubt- 

 less, even gases, would become permanently solid, 

 and all motion on the surface of the earth would be 

 arrested.* 



Now, as there is a continual change of tempera- 

 ture in all bodies on the surface of the globe, it fol- 

 lows that there is a continued change of magnitude. 

 The substances surrounding us are constantly swell- 

 ing and contracting under the vicissitudes of heat 

 and cold. They grow smaller in winter and larger 

 in summer. They swell their bulk in a warm day 

 and contract it in a cold one. Thus we see that in 

 warm weather the flesh swells and the vessels ap- 

 pear filled ; in cold weather the flesh contracts, the 

 vessels shrink, and the skin shrivels. 



When water freezes it becomes lighter, and 

 therefore swims ; were it not for this circumstance, 

 our lakes and rivers would all become solid bodies 

 of ice during the winter. Caloric is given from 

 substances when freezing, which tends to mitigate 

 the severity of cold. For this reason we feel 

 warmer after a heavy fall of snow. Ice thaws 

 very gradually ; were it not so, the most alarming 

 inundations would follow. 



Heat is measured by means of the thermometer. 

 This is merely a graduated glass tube, containing 

 quicksilver, alcohol, or other substances which do 

 not readily freeze. After the fluid is introduced, 

 the air is expelled by heating the bulb, when the 

 tube is hermetically sealed ; then, by immersing it in 

 boiling water, the mercury rises to a certain point, 

 which is marked; afterward it is immersed in a 



* Turner's Chemistry. 



