The foregoing paper was read on 5th July 1880. We postponed, however, its publication, feeling that however interesting the formation of the bodies therein described might be, much careful quanti tative research would have to be undertaken before any definite conclusion as to the true nature of these bodies could justifiably be drawn. Only the title of our paper was therefore published in the Proceeding of this Society. The old University Laboratory being in many respects'unfitted for the prosecution of accurate quantitative work, our researches were repeatedly postponed in the hope of being able to continue them in the new University Laboratory, which, however, only now approaches completion. This delay has been to us a subject of much regret, the questions involved being of no little interest.