Classic Poem

I am a shepherd of those sheep
That climb a wall by night,
One after one, until I sleep,
Or the black pane goes white.
Because of which I cannot see
A flock upon a hill,
But doubts come tittering up to me
That should by day be still.
And childish griefs I have outgrown
Into my eyes are thrust,
Till my dull tears go dropping down
Like lead into the dust.