Hi Millard,
I'm sure the problem is that your pothos is rootbound and needs a 2" larger pot.* That is why is perks up when it's out in the rain.* Generally yellowing leaves with a houseplant mean that a plant is rootbound.* Leaves are expendable to a plant and they will shed the ones they can't support.* You will probably have to tease the roots a bit as they are probably winding around and around in a tight ball.* This is a tough plant, so you can massage the outer layer of roots to loosen them.* Here's how to repot.
http://www.ourgardengang.com/containerpotting.htm
http://www.dirtdoctor.com/view_question.php?id=70
You will also find that pothos do lose their lower leaves as they grow, so your only hope of keeping it full will be to start new plants from cuttings.* I do that with mine every few years to refresh it.* In the wild in the jungle this plant grows as a vine up trees, losing it's lower leaves as it grows.* Don't overwater this plant.* I often remember to water after it's wilted a bit.
http://aggie-horticulture.tamu.edu/i...um_aureum.html
Newt
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.