Empedocles thought that the 4 substances  fire, solids, liquids, and air  are  elements of the universe that  causing the universe to die and reborn, (today we know that earth elements can change with appropriate temperature to solid, liquid, and air).
He believed that planets twirling around the Sun and not falling in to it was in fact of two forces
«Φιλότης, and Νεϊκος» 

Φιλότης- Philotis =friendliness - attractiveness (=Gravity by Isaac Newton).
Νεϊκος - neikos = escapee - unfriendly (=Centrifugal force).      
The orbital direction of the universal bodies according to Empedocles. As a result to the two opposite forces (Φιλότης and Νεϊκος) the attracted body is finely forced to an endless circling movement.