Answer:
Humans have two that shrink in the light and expand in the dark
What is at the end of a rainbow?
Power enough to smash ships and crush roofs. Yet it still must fear the sun.
The part of the bird, that is not in the sky, Which can swim in the ocean and always stay dry. What is it?
I am a king but also a common device of measure. What am I?
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.