This is the title page of Mario Bettini’s *Aerarium Philosophiae Mathematicae* [*Treasury of Mathematics*], published in 1648. Bettini (1582 - 1657) was a Jesuit, a mathematician and a well respected astronomer. This book is an encyclopedic collection of mathematical curiosities.

The frontispiece of Bettini’s book. The picture is a pun on the title, *The Treasury of* *Mathematics*. The picture shows a Prince providing a Jesuit with a chest of money. The Jesuits are thus paid to provide the common people with knowledge of mathematics.

Pages 48 and 49 of Bettini’s *Treasury* discuss the generation of a spiral as a path around the surface of a cylinder. The diagram on page 49 shows that if a spiral is unrolled from its cylinder it will revert into the hypotenuse of a right triangle.

Pages 74 and 75 of Bettini’s book illustrate the erroneous use of simple geometry in determining the diameter of the sun.

A fold-out plate from Bettini’s book provides views of various solids and nets for the construction of polyhedra.