Who among the following thinkers observed that light and heat are only different forms of the same essential substance and also spoke of gravity as the cause of falling?

The thinker described is Kanad, the founder of the Vaisheshika system.

He held light and heat to be different forms of one underlying substance (tejas).

He also identified gravity (gurutva) as the cause of a body's falling.

These physical observations belong to the atomistic Vaisheshika tradition he began.

Such reflections on light, heat and falling mark Kanad's naturalistic inquiry.