Sentence:  ... after a little way out to sea, there was a current and wind, always one way in the morning, the other in the afternoon. This I understood to be no more than the sets of the tide, as going out or coming in; but I afterwards understood it was occasioned by the great draft and <WSD>reflux</WSD> of the mighty river Orinoco ... 
Meaning of the word marked with <WSD> tags:  The backwards flow of any fluid.