What are The Four Great Elements? Can someone provide a comprehensive explanation, on what the four great elements are and how they work and exist?

I also have a special interest about the "mobility-element", in the four great elements.

I am interested in Theravada teachings.
The 4 elements are: 


pruṭhavī-dhātu - solidity or attraction. This holds something together. You feel this as tightness, pressure in the body.
āpa-dhātu - liquidity or relative motion. See below.
teja-dhātu - heat or energy. Body temperature, vibrations in the body you feel in meditation. Difference of temperature in and out meditation.
vāyu-dhātu - expansion or repulsive forces. You feel this as pulsation or expansion and contraction in the body or flow of respiration, rumbling gasses in the belly and passing of wind.


Mobility element is liquidity like liquidly nature in the nose, saliva, urine, sweat. You can look at the flowing nature of these elements in mediation. Though solidity, heat, air element can be experienced through the body liquidity can be experienced or constructed through the mind only.

More particularly, the experience of the 3 elements (earth, heat, air) are happen through Body - Conciousness accompanied by either Pain, Pleasure, or Neutral Sensation and liquidity (motion) through the mind. 

Some translators translate Air Element (vāyu-dhātu) as motion element. 

Also see: Matter and Moments, Matter &amp; moments and feeling 1, Rupa (Form), Lectures on Rupa 1a, 1b, 1c, 1d, 2a, 2b, 2c, 2d by Piya Tan for more academic analysis of the Elements. Wikipedia entry on Mahābhūta.