"They produced something that existed only in theory."
If they had added [up until that point] it would perhaps be clearer, but it is quite implied. Ie, it was theorized up until it was then proven to exist.
Edit: Air, and it's various elements, was also at one time theoretical.
Reading comprehension.
"They produced something that existed only in theory."
If they had added [up until that point] it would perhaps be clearer, but it is quite implied. Ie, it was theorized up until it was then proven to exist.
Edit: Air, and it's various elements, was also at one time theoretical.
You’re right. I didn’t read it correctly.