34 
pulsive energy of. heat , and the harmonious cycle 
of terrestrial changes is produced by their mutual 
operations. 
Heat is capable of being communicated from 
one body to other bodies ; and its common effect 
is to expand them, to enlarge them in all their di- 
mensions. This is easily exemplified. A solid 
cylinder of metal after being heated will not pass 
through a ring barely sufficient to receive it when 
cold. When water is heated in a globe of glass 
having a long slender neck, it rises in the neck ; 
and if heat be applied to air confined in such a 
vessel inverted above water, it makes its escape 
from the vessel and passes through the water. 
Thermometers are instruments for measuring de- 
grees of heat by the expansion of fluids in nar- 
row tubes. Mercury is generally used, of which 
100,000 parts at the freezing point of water become 
101,835 parts at the boiling point, and on Fahren- 
heit’s scale these parts are divided into 180 de- 
grees. Solids, by a certain increase of heat, be- 
come fluids, and fluids gases, or elastic fluids. 
Thus ice is converted by heat into water, and by 
still more heat it becomes steam : and heat disap- 
pears, or, as it is called, is rendered latent during 
the conversion of solids into fluids, or fluids into 
gases, and re-appears or becomes sensible when 
gases become fluids, or fluids solids ; hence cold 
is produced during evaporation, and heat during 
the condensation of steam. 
There are a few exeptions to the law of ex- 
pansion of bodies by heat, which seem to depend 
either upon some change in their chemical con- 
