An early reference to the Pierian spring is found in the Satyricon of Petronius from the late 1st century AD:
"This is the right armour of genius–
'Drink deep or taste not the Pierian spring.'
Only then pour out your heart."
Lines 215 to 232 of Pope's poem read:
"A little learning is a dang'rous thing;
Drink deep, or taste not the Pierian spring:
There shallow draughts intoxicate the brain,
And drinking largely sobers us again.
Fir'd at first sight with what the Muse imparts,
In fearless youth we tempt the heights of Arts,
While from the bounded level of our mind
Short views we take, nor see the lengths behind;
But more advanc'd, behold with strange surprise
New distant scenes of endless science rise!
So pleas'd at first the towering Alps we try,
Mount o'er the vales, and seem to tread the sky,
Th' eternal snows appear already past,
And the first clouds and mountains seem the last;
But, those attain'd, we tremble to survey
The growing labours of the lengthen'd way,
Th' increasing prospects tire our wand'ring eyes,
Hills peep o'er hills, and Alps on Alps arise!"
The Divine Comedy's Empyrean, illustrated by Gustave Doré
Click to enlarge these images.
http://en.wikipedia.org/wiki/Empyrean