short story problem

im after a book that contained three short stories. unfortunately i have no
idea what these three short stories was called, and the only author i can
remember the name of in john wyndham.

I know the one of the stories was concerned with a ship making an emergency
landing on a planet that had some mysterious power

one of the stories was about a man who became invisible and his
'adventure'...one of the characteristics of this story i particularly
remember was the fact that the man could not stand still or he would sink
into the earth. i think this is the short story john wyndham wrote

the third short story was about two children who found a 'wormhole' to
another planet by semi-accident and get transported there and deal with the
strange beings there and then somehow make it home.

if anyone out there can remember the names of these short stories or the
authors names or anything, PLEASE let me know....i have been looking for
this book for years now and to no avail.

thanks