The Rainbow a Riddle

A bridge weaves its arch with pearls

High over the tranquil sea

In a moment it unfurls

Its span, unbounded, free.

The tallest ship with swelling sail

May pass beneath its arch with ease;

It carries no burden, 't is too frail,

And with your quick approach it flees.

With the flood it comes, with the rain it goes;

What it is made of nobody knows.