Drawing negative space

The next exercise in The Book is learning how to draw negative space. That's the space around objects, rather than the object itself. And, to be honest, I'm struggling a bit with this one. Apparently you're supposed to look at the object and then look "through" it to see the negative space surrounding it. If you then draw the negative space, this will help you with things like proportionality and sizing.

This is something I do struggle with in my sketching - how to size objects appropriately to keep the relative proportions and also so that I don't end up running out of space on the page. But having tried out these exercises, I still seem to be unable to get the size of whatever it is I'm drawing right. Hmm...

Here are my efforts:

As you can see, I got totally fed up with the last one and gave up halfway through. The table is a bit better, but still not great. I think I might have drawn it better if I'd been looking at the table, and not the space around the table... But that wasn't the point of the exercise ;)

If anything good came out of this exercise, it's that I'm quite happy with the shading on the chair in the first picture. The exercise was to shade in the background first with graphite and then draw the chair over the top (I don't know why) but because I didn't have any graphite, only charcoal, it didn't quite turn out as planned. But after I'd drawn the chair, I used an eraser to highlight the chair. And I'm pretty happy with the result.

In the meantime, I'll have another go at drawing negative space.