Complex sentence: He theorized that matter could not be destroyed, see Law of conservation of matter and was also interested in the question of why water experiences difficulty flowing out of a container that has been turned upside down, see atmospheric pressure and vacuum.
Split into simpler sentences: He theorized that matter could not be destroyed, see Law of conservation of matter. Also the interesting question of why water experiences difficulty flowing out of a container that has been turned upside down, see atmospheric pressure and vacuum.