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A CRITIQUE
125
tain conditions of temperature, pressure, etc Within the body, the molecules themselves are in a state of agitation This motion of molecules of any material substance is known as heat motion or thermal motion, for the simple reason that it is responsible for the phenomenon of heat For, it is molecular motion that produces a certain irritation in the nervous fibres of our sense of touch and produces the sensation that we call heat This thermal motion exists in solid, liquid and gaseous states of matter because the amount of energy in every molecule is the same for all substances at a given temperature and the only difference is that while in some case the molecules are able to move around, in other cases they can only vibrate in fixed position This thermal motion appears to be an instance of vyanjana paryāya
PARINAMA
Physical properties like extension (volume) mass, density, etc, can be changed by change in temperature and or pressure For instance water is solid (in the form of ice) at temperature 0°C or below When heated it becomes liquid and its volume slightly increases At 100°C it boils and changes into steam which has very much larger volume Similarly air (or oxygen) which is gaseous at normal temperature and pressure can be liquified under very high pressures The thermal motion in a solid body is quivering or 23 vibration of molecules If the body is heated the quivering becomes stronger and at the melting point the molecules leave their places and begin to move At still higher temperatures they fly apart in all
23 Temperature of liquid air is 63° absolute or 210° C below
zuro
