I think the general population always knew that there was a transparent substance all around them which had to keep going in and out of their lungs or they would die - the “the breath of life” from the Bible. I mean, even an uneducated peasant in ancient times could blow bubbles underwater and see that there was something coming out of his mouth.
I think you underestimate our past ignorance. It took many decades of science being taught for the general population to “know” that air exists.
I think the general population always knew that there was a transparent substance all around them which had to keep going in and out of their lungs or they would die - the “the breath of life” from the Bible. I mean, even an uneducated peasant in ancient times could blow bubbles underwater and see that there was something coming out of his mouth.