Abstract
The author in an address recently published put forward evidence for regarding the benzene ring as an actual structure of ascertainable size and form, and deduced that the unit cells of naphthalene and anthracene should have two of their axes equal, the third axis being longer for anthracene than for naphthalene by the width of one ring. The experimental data then available supported this hypothesis only roughly; in the present Paper it is shown that more reliable data, subsequently obtained from small but perfect anthracene crystals, agree with it very closely. It is pointed out that the X-ray data furnish a new and accurate method of determining the density of a crystal.