CALORIC. 



31 



bodies. This may be illustrated by the following 

 examples : If a flaccid bladder be tied at the mouth 

 and held near the fire, it will swell and become fully 

 distended by the rarefaction of the contained air. 

 In fixing the tire on to the wheels of carriages, the 

 rim of iron is made at first of a diameter somewhat 

 less than that of the wheel; but, by being after- 

 ward heated, its circumference is so much increas- 

 ed that it will be sufficient to embrace and surround 

 the wheel. When placed upon the wheel, it is 

 cooled, and, suddenly contracting its dimensions, 

 binds the wheel firmly together, and becomes se- 

 curely fixed in its place. If the stopper of a glass 

 bottle or decanter becomes so firmly fixed in its 

 place that it cannot easily be removed, by wrapping 

 the neck of the vessel round with a cloth dipped in 

 hot water, we cause the glass to expand, and the 

 neck will be enlarged so as to allow the stopper to 

 be easily withdrawn.* 



By the application of the same principle, the 

 walls of a large building, which had been forced out 

 of the perpendicular by the weight of the roof 

 were drawn together by heating bars of iron, which 

 were placed across the building at right angles to 

 the walls. By means of nuts screwed on their 

 ends outside of the building, which were tightened 

 as the rods were alternately heated and cooled, the 

 walls were easily drawn into their original perpen- 

 dicularity. As air or water become heated, they 

 become lighter and ascend ; in this manner water is 

 made to bpil, the air of our rooms becomes uniform- 

 ly warmed, and the atmosphere is purified by the 

 incessant motion caused by rarefaction. Thus we 



perceive it is not at all strange that a quantity of water and 

 clay should occupy a larger space than the clay alone. Thus 

 the elastic vapour of steam occupies more space than the water 

 when condensed. 



* Lectures on Geology, by Von Leonhard, translated by Mor- 

 ris, p. 61. 



