Didn't know about "Atom" reaching #1 on the charts
but always assumed it was one of those albums that folks had cooled on over the years. Have a friend who's in his 60's and loves the album as much as I do and always makes it sound like the album was pretty popular when it first came out. Though to be fair, part of the sales might have been simply due to the packaging which was pretty noticeably avant garde for the time. And as I've said before, the title suite is an ideal soundtrack for tripping, which is what a lot of Floyd fans wanted, at least in those days.