In 1891 Nikola Tesla stated:

Tesla continues:

When you think about empty space, what comes to mind ?
If you're thinking is similar to 18th Century science then you proably assume that in the deep voids of space there is a whole lot of emptiness. You believe that empty space is just that: empty.

And indeed, a visual observation using our very own eyes reveal two clearly distinct things: solid objects and empty space.

Looking through the lens of a telescope, this observation tends to reveal the same thing: in deep space there is solid matter (stars, planets, dust) and huge regions empty space.