> A constant implied that it had identified two proportional quantities — in this case, period squared and distance cubed. In other words, it stopped when it found an equation.

Very interesting article. Thanks for posting.

I've been thinking about the physics equation and its relation to proportionality. Not all physics equations are proportionalities because in physics the equality sign is loaded.

To me, proportionality is fundamental not the physics equation. So I would have written the last sentence of the quote as "...it stopped when it found [a proportionality].