What is the difference between は and のは?


The following sentence means "seeing all the different foreign people was
interesting."

This, according to my Japanese friends is incorrect:

> 色々な外国人を見ているは面白かった。

... and this is correct:

> 色々な外国人を見ているのは面白かった。

To me, the difference is so subtle that I can't really get a feel for how the
presence of の really changes it.

Can someone provide an explanation that clarifies what makes の important in
this situation?

Update: I'm actually still confused by this. Couldn't the first example mean
"Looking at the various foreigners was interesting", and the second example
mean "That I was looking at the various foreigners was interesting"?




In this case, 「の」 changes the verb "to [be] see" into the
[gerund](http://en.wikipedia.org/wiki/Gerund) form "[be] seeing", which is
what you found interesting. After that, 「は」 is just 「は」.




In this case, 「の」 changes the verb "to [be] see" into the
[gerund](http://en.wikipedia.org/wiki/Gerund) form "[be] seeing", which is
what you found interesting. After that, 「は」 is just 「は」.

