Which form of heat believed in before the modern times ?

Explanation

Before the modern picture, heat was regarded as a fine invisible fluid (called caloric) filling in the pores of a substance.
On the contact between a hot body and a cold body, the fluid (called caloric) flowed from the colder to the hotter body.
In the caloric picture of heat, heat flows until the caloric levels (i.e. the temperature) equalise.