From an Epistle to Mira

Of substance I've thought, and the varied disputes
On the nature of man and the notions of brutes;
Of systems confuted, and systems explain'd;
Of science disputed, and tenets maintain'd.
These, and such speculations on these kind of things,
Have robb'd my poor Muse of her plume and her wings;
Consumed the phlogiston you used to admire,
The spirit extracted, extinguish'd the fire;
Let out all the ether, so pure and refined,
And left but a mere caput mortuum behind.