I. On the structure of rubies, sapphires, diamonds, and some other minerals

For many years Mr. Butler has had the opportunity of examining very many rubies, sapphires, and diamonds, and has taken advantage of it in forming a most interesting collection, cut and mounted as microscopical objects. He had very carefully studied the included fluid-cavities, and ascertained many curious facts. Mr. Sorby had for some time paid much attention to the microscopical structure of crystals, and published a paper in which he showed that their microscopical characters often serve to throw much light on the origin of rocks. Mr. Butler therefore placed the whole of his collection in Mr. Sorby’s hands for careful examination, and it was decided that a paper should be written by the two conjointly ; and since Mr. Sorby had previously made many experiments in connexion with the expansion of liquids, as already described in a paper published in the Philosophical Magazine, he took advantage of the opportunity to investigate the law of the expansion of the very interesting fluid met with in the cavities of sapphire. In describing the various facts, it will be well to consider them in relation to the following general principles :— (1) The structure of the various minerals as mere microscopical objects. (2) The physical characters of the fluid-cavities, as throwing light on the origin of the minerals. (3) The influence of some included crystals on the structure of the surrounding mineral.