The sun finally decided to come back out from behind the clouds, and we were able finish up our water balloon, magnifying glass investigations.
First off, we confirmed again, that while we could not heat the water inside the balloon as we had by holding a water balloon over a flame (click here to read about that), the balloon still would not pop, like our air-filled balloons had, with a direct beam of sunlight focused on it, unless...
...we focused the sunlight directly onto the air bubble inside the water balloon.
Then, the balloon burst as instantly as our air filled balloons had before, but with a sudden splash instead of the ear splitting "pop".
Once you focus the beam of light onto the air bubble, the balloon pops almost instantly, drenching the person doing the popping, and startling everyone else. It's a little like playing with a Jack-in-the-box, terrific fun if you have the nerve for it.