When the green woods laugh with the voice of joy,
And the dimpling stream runs laughing by;
When the air does laugh with our merry wit,
And the green hill laughs with the noise of it;

when the meadows laugh with lively green,
And the grasshopper laughs in the merry scene,
When Mary and Susan and Emily
With their sweet round mouths sing "Ha, ha he!"

When the painted birds laugh in the shade,
Where our table with cherries and nuts is spread:
Come live, and be merry, and join with me,
To sing the sweet chorus of "Ha, ha, he!"

Source and related links:

blakearchive.org/exist/blake/archive/object.xq?objectid=songsie.z.illbk.15
http://en.wikipedia.org/wiki/Laughing_Song