On Rarity of a Book - Searching SOLO for 2 of my books

This is purely an excercise for the uninitiated!

Rarity is the number of books available across libraries (as a measurement) worldwide!

These books are from my collection:

1. 1725, A Sacred Poem, View of Death, The Soul's  Departure from the World, by J. Reynolds

From the above it's evident that there are only about 4 books available across 4 libraries; worldwide

Now, my other set:

1799, The Works of Sir William Jones

From the above it's evident that are a minimum of 4711 books in libraries across the world.

Hence, checking the Rarity of your books is imperative of how valuable your collection is!