[coldtea]

>I don't see much in the article to persuade me that da Vinci was equating gravity and acceleration in the way Einstein did

Thinking of the effect on speed of things falling down as acceleration (as opposed to constant), and even coming up with a formula, is already a bridge between these two things.

[Gregaros]

No, it is not at all a bridge to Einstein’s ‘gravity and acceleration are equal’, which is "the gravitational force is physically indistinguishable from any acceleration", which has to do with changing to relatively accelerating reference frames.

The insight of da Vinci’s here is anticipating Newton, not Einstein. And yes, this is already an accomplishment, but not the outlandish one the article would imply.

[coldtea]

Hence "a bridge". It's not Einstein's result, but it's moving towards Netwon (and eventually that) from older ideas about the behavior of things "falling" (such as proportional to their weight and constant speed).