What Does St. Francis de Sales Mean by "Sounding Periods" in Sermons?

In St. Alphonsus Liguori's *Dignity and Duties of the Priest,* it is written: > Empty words and sounding periods are, says St. Francis de Sales, the pest of sermons. (*De la Predic.* ch. 5, a. I.) First, because God does not cooperate with vain preaching.... Does anyone know what St. Francis may have meant by the expression, "sounding periods"? Also, what is the referenced work, *de la Predic.*?