Page:The Elements of Euclid for the Use of Schools and Colleges - 1872.djvu/315

Rh The rule for the volume of a prism involves the fact that prisms, on equal bases and between the same parallels are equal in volume.

A parallelepiped is a particular case of a prism. The volume of a pyramid is one third of the volume of a prism on the same base and having the same altitude.

For an account of what are called the five regular solids the student is referred to the chapter on Polyhedrons in the Treatise on Spherical Trigonometry.

THE TWELFTH BOOK.

Two propositions are given from the twelfth Book, as they are very important, and are required in the University Examinations. The Lemma is the first proposition of the tenth Book, and is required in the demonstration of the second proposition of the twelfth Book,