 After retiring in 1969, he taught for a semester at Carlton College in Minnesota before returning to Wales, where he helped  write articles for the 1974 edition of the Encyclopædia Britannica.
<fluency>  After retiring in 1969, he taught for a semester at Carlton College in Minnesota before returning to Wales, where he helped  write articles for the 1974 edition of the Encyclopædia Britannica.
 After retiring in 1969, he taught for a semester at Carlton College , Minnesota, before returning to Wales, where he helped write articles for the 1974 edition of the Encyclopædia Britannica.