Answer:
What can be measured but not seen?
What can go through glass without breaking it?
I have four legs but no tail. Usually I am heard only at night.
Twigs and spheres and poles and plates. Join and bind to reason make.
It flies when it's on and floats coming off.
I am your mother's brother's only brother in law. Who am I?
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?