Good start, Hesperis! It took me about 20 minutes of false starts last night before I came up with the "dog" one all of a sudden. Try prayer. It might work.

I sweated for ages over one that started...

An insane physicist from L.A.
Tried to measure the whole Milky Way
First he ran out of tape
Then his lab rats escaped
Now he's.... Someone finish it, please? And don't screw up the meter!