16 CALORIC, HEAT, FIRE. 



caloric will pass from the body to our hand, and this 

 will produce the sensation of heat : but if we touch a 

 body colder than our hand, the contrary will take place ; 

 the caloric will be abstracted from our hand, and we 

 shall experience the sensation of cold. Some bodies are 

 found to transmit caloric more easily than others ; they 

 are thence called conductors of caloric : some do not 

 transmit it at all, or in a very trifling degree, and these 

 are called non-conductors of caloric. The best conductors 

 are the metals ; the worst conductors are fur and caout- 

 chouc. Air is also a bad conductor, and so is water. 



One of the principal effects of caloric is expansion ; and 

 this is evident in all kinds of bodies, whether solid or 

 fluid, but varying in degree. Thus, as it regards solid 

 bodies, lead is more expansible than iron, and iron than 

 platina. In order to show the expansion of metals, let a 

 round piece of iron, which has been made to fit a ring 

 exactly when cold, be heated, and it will be found so in- 

 creased in bulk as to be too large to pass through the 

 ring. The expansion of fluids is prettily shewn by filling 

 a Florence flask with cold water to about the middle of 

 the neck, and suspending it over a lamp ; as it grows 

 hot it will be found to expand gradually, so as nearly to 

 flow over the neck of the flask. The principle of the 

 thermometer depends on the expansive power of caloric ; 

 in proportion as the temperature increases, the quick- 

 silver or alcohol,* whichever it may contain, expands in 

 proportion. Water in becoming frozen forms somewhat 

 an exception to the above ; for when it is cooled to a 

 temperature of about 40 it begins to expand, and con- 

 tinues to do so until it becomes solidified into ice.f The 

 wisdom of this contrivance it strikingly evident ; for if 

 water followed the general law, and when frozen became 

 of less bulk, and consequently of a greater relative 

 weight, it would sink to the bottom as it was formed on 

 the surface, and in the course of time the ocean, to a 

 considerable extent, in the higher latitudes, as well as the 



* In the higher latitudes thermometers containing coloured alcohol 

 are used, as in intense cold the quicksilver may become frozen, 

 f When water is frozen, the crystals form at an angle of 60". 



