Sentence:  An untaught peasant beheld the elements around him and was acquainted with their practical uses. The most learned philosopher knew little more. He had partially unveiled the face of Nature, but her immortal lineaments were still a wonder and a mystery. He might dissect, anatomize, and give names; but, not to speak of a final cause, causes in their secondary and <WSD>tertiary</WSD> grades were utterly unknown to him. 
Meaning of the word marked with <WSD> tags:  Of third rank or order; subsequent.