Sentence:  [V]apors are never attracted or drawn up above the middle Region of the Air; for that the cold Air there, by thickning and <WSD>conglomerating</WSD> them, preſently turn them into clouds: and thence proceeds Miſts, Rains, Snows, Hayls, &c. 
Meaning of the word marked with <WSD> tags:  To combine together into a larger mass.