Sentence:  The last Mr. Hobbs's principal explanations, is of the experiment wherein above 100 pound weight, being hung at the depress'd <WSD>sucker</WSD>, the <WSD>sucker</WSD> was, notwithstanding, impell'd up again, by the air, to the top of the cylinder. 
Meaning of the word marked with <WSD> tags:  The embolus, or bucket, of a pump; also, the valve of a pump basket.