1S13.] Philosophical Transactions for 1S13. Part I. 229 



consequence of which the sides of the eye collapse, and its axis 

 from the cornea to the retina is lengthened ; by which alteration 

 the length of this axis is brought into the same proportion to the 

 flattened state of the cornea, or crystalline, or both, which it 

 had to these parts before the alteration took place. 



V. The Bakerian Lecture. On the Elementary Particles of 

 certain Crystals. By William Hyde Wollaston, M.D. Sec. R.S.] 

 The regular octahedron is well known to crystallographers to 

 constitute the primitive form of a considerable number of mine- 

 rals. Now there is a difficulty with respect to the figure of the 

 integrant molecules of such bodies. The octahedron may be 

 divided into octahedrons and tetrahedrons, and the same obser- 

 vation applies to each of the tetrahedrons thus obtained ; so that 

 two different figures present themselves. If we make choice of 

 the tetrahedron, we must suppose the body full of octahedral 

 spaces; and if we adopt the octahedron, the body must be full 

 of tatrahedral spaces: and the molecules, whether octahedral or 

 tetrahedral, must unite by their edges instead of their faces. 

 These suppositions, it must be obvious, are of such a nature as 

 not to be satisfactory. Dr. Wollaston gets over the difficulty by 

 supposing the integrant molecules in such cases to be spherical: 

 and he shows how spherical molecules are capable of forming 

 tetrahedrons, octahedrons, and rhomboids. He shows, also, 

 that rhomboids would be the result of the union of oblate sphe- 

 roids. Oblong spheroids, on the contrary, would form three 

 and six-sided prisms. He shows how cubes might be the re- 

 sult of the union of two sets of spherical particles, each set 

 foriuing a tetrahedron. 



VI. On a Substance from the Elm-tree, called Ulmin. By 

 James Smithson, Esq. F.R.S] The substance to which I gave 

 the name of ulmin, was examined by Klaproth about a dozen of 

 \(.us ago. and the account of its properties which 1 gave in my 

 System of Chemistry was taken without alteration from Klap- 

 roth's paper. More than two years ago, however, 1 had satisfied 

 myself, by the examination of some ulmin from Plymouth, that 

 Klaproth s account was in several respects inaccurate, and that it 

 had been the result of a very hasty and imperfect examination of 

 the substance in question. My experiments were published in 

 the first number of the Annals of Philosophy. Mr. Smithson's 

 experiments, having been made upon a portion of the same 

 Palermo ulmin which Klaproth examined, remove every doubt 

 respecting the properties of this peculiar substance. Palermo 

 Ulmin, in lumps, appears black; but in thin pieces it is trans- 

 parent, and ot a deep red colour. It dissolves readily in water; 

 the dilute solution is yellow; the concentrated, the colour of 



txL This solution appears to be a combination of potash with 

 a peculiar .substance, to which the name of ulmin may be given. 



