Optical illusion

Was tidying my bookshelf. Space is a bit tight, so I wondered if stacking books vertically might help.

I looked at my RJ Anderson books. A row of 7 books.

(ignore the shelf labels. They are left over from a youthful attempt to label all my books like they were in a library.)

Since the row is longer than the books are tall, I could save space by rotating them and stacking them vertically.

So I did.

It's shorter.

This is a scientific fact, proven by experimentation.

I still don't believe it.