[Moonman62]

So was Newton’s until Einstein came along.

...

Or until somebody noticed Mercury’s orbit wasn’t what it was predicted to be.

This anomalous rate of precession of the perihelion of Mercury’s orbit was first recognized in 1859 as a problem in celestial mechanics, by Urbain Le Verrier. His reanalysis of available timed observations of transits of Mercury over the Sun’s disk from 1697 to 1848 showed that the actual rate of the precession disagreed from that predicted from Newton’s theory by 38 (arc seconds) per tropical century (later re-estimated at 43” by Simon Newcomb in 1882).

[FredZarguna]

I can't put my finger on my notes at the moment, but I believe James Clerk Maxwell had already fired the first salvos against Newtonian Physics a few years before that. Very close to 1859, it became obvious before Maxwell first published his unified theory of the electromagnetic field that electromagnetic induction was what would later come to be known as Lorentz Invariant and that Newtonian Mechanics was not.

There was even a period before the Special Theory of Relativity when physicists would say "everything obeys Newtonian mechanics, except for electric current."

[farming pharmer]

Or until somebody noticed Mercury’s orbit wasn’t what it was predicted to be.

This anomalous rate of precession of the perihelion of Mercury’s orbit was first recognized in 1859 as a problem in celestial mechanics, by Urbain Le Verrier. His reanalysis of available timed observations of transits of Mercury over the Sun’s disk from 1697 to 1848 showed that the actual rate of the precession disagreed from that predicted from Newton’s theory by 38 (arc seconds) per tropical century (later re-estimated at 43” by Simon Newcomb in 1882).

I first heard about this in one of the 'Titanium Physicists' podcasts, which I highly recommend.