SECTION II. 
OF THE NATURE AND PROPERTIES OF STEAM, ITS ELASTIC FORCE, 
EXPANSIVE FORCE, AND POWER OF MOTION. 
Art. 65. Natural bodies exist in three states; the solid, the liquid, and the 
gaseous. The state of many of them may be changed : thus, water may be in the 
solid state as ice, in the liquid as water, in the gaseous as steam, and these 
changes take place only under particular degrees of heat and pressure ; but there 
are some gaseous bodies which cannot be reduced to the liquid form by the means 
we at this time are acquainted with ; though there has been so much accomplished 
as to render it tolerably certain, that all the gases known would be reduced to 
liquids, were they exposed to sufficient pressure and reduction of temperature. 
66. Those gases which are not changed into liquids by the ordinary changes 
of temperature and pressure, are called permanent gases. 
The gases which condense into liquids by the common changes of temperature 
and pressure, are called vapours, or steams : we shall use the term c steam’ in 
preference to ‘vapour.’ 
67. Heat, free and uncombined, is diffused through all bodies in nature, 
whether they be in the state of solids, liquids, or gases; and it constantly tends to 
an equilibrium ; so that, when by any means it is accumulated in particular sub 
stances, a portion is quickly given off to the surrounding bodies, so as to bring the 
whole to one common temperature. On the other hand, where bodies have been 
deprived of a portion of it, heat is given off to them by, or heat passes to them 
from, the surrounding bodies, to restore the equilibrium. 
68. When there is an equilibrium of heat, or the adjoining bodies are of the 
same temperature, if it be destroyed by the introduction of a fresh quantity of heat, 
different bodies will be found to absorb different quantities of the new portion of 
heat in restoring the equilibrium. The peculiar quantity which each body absorbs 
under the same circumstances, is denominated the specific heat of that body. In