Ye living lamps, by whose dear light
The nightingale does sit so late,
And studying all the summer night,
Her matchless songs does meditate;
Ye county comets, that portend
No war nor prince's funeral,
Shining unto no higher end
Than to presage the grass's fall;
Marvell could be referring to the move away from the subjective, as he suggests that comets (typically used to tell the future), could merely predict the fall of the grass. He suggests that the glow worms (something physical), is something that is better, showing more scientific and logical Renaissance beliefs of the time.
The Mower to the Glow-Worms