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be easily withdrawn.* 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 apphcation 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 boil, 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. 
