At Purdue , he began working with his doctoral advisor , Harry Pollard , because of a shared interest in pedagogy .
At Purdue , he soon picked up Pollard 's interests in celestial mechanics and wrote his doctoral dissertation on the n - body problem .
At Purdue , he began working with his doctoral advisor , Harry Pollard , because of a shared interest in pedagogy , but soon picked up Pollard 's interests in celestial mechanics and wrote his doctoral dissertation on the n - body problem .