Edward was explaining the basics of the experiment as they worked. How the deliberate spacing and setting of the stakes to the right height, would change the way the sun cast a shadow on them. By using those measurements over the course of a few weeks and even years you could chart the course of the sun through the sky. While the only one there that could actually understand the explanation was Ruth, Edward constantly checked to see if Jacob was listening as well. His gaze flicked to the babe as he kept the language so simple that a child could have understood it... though not a baby.