Full Idea
The name 'energy', first used by Thomas Young, has come into use after it was raised from a mere formula of mathematical dynamics to become a principle pervading all nature, and guiding every field of science.
Gist of Idea
Energy has progressed from a mere formula, to a principle pervading all nature
Source
Lord Kelvin (Wm Thomson) (works [1881]), quoted by Peter Watson - Convergence 01 'Principle'
Book Reference
Watson,Peter: 'Convergence' [Simon and Schuster 2016], p.28
A Reaction
[bit compressed] As far as I can see energy behaves exactly as if it were a substance, like water conserved in rainfalls, and yet it isn't a stuff, and seems to result from a process of abstraction. I take it to be one of the biggest mysteries in physics.