XXVI. Notice of the Progress of Botanical Science in Ben- gal, being the substance of a Letter from Dr WALLICH, Superintendant of the Botanical Gar- den near Calcutta, to FRANCIS HAMILTON, M. D. XXVII. Notice respecting Barystrontianite, a New Mine- XXVIII. Account of a singularly Poisonous Insect which destroys Horses. By the Rev. ELIAS CORNELIUS, 381 390 XXX. Account of the new Binary Galvanic Pile, invented XXXI. Account of a remarkable Comet which has return- ed to our system in 1786, 1795, 1801, 1805, and 1818, XXXII. Notice respecting the Discovery of the Skeleton of a Whale on the estate of Airthrey, near Stirling. By ROBERT BALD, Esq. F. R. S. E. &c. XXXIV. Account of the large Comet of 1819, XXXV. Quarterly Abstract of the Diurnal Variation of the Magnetic Needle. By Colonel BEAUFOY, F. R.S. 403 XXXVI. Proceedings of the Royal Society of Edinburgh, 404 XXXVII. Proceedings of the Wernerian Natural History So- 4.07 OPTICS. 3. Captain Colby on a curious instance of unusual Refraction. 4. M. Chossat on the Form of the Cornea and Crystalline Lens in the Eyes of Oxen, &c. MAGNETISM. 5. M. Wleugel on the Variation and Inclina- tion of the Needle at Copenhagen, ACOUSTICS. 6. Subterraneous sounds in Granite rocks, 413 GALVANISM. 7. Improvement upon the dry Pile of Zamboni. 10. MM. Dulong and Petit on the Relation between the spe- cific heat of bodies, and the weight of their atoms. 11. Sin- gular Heat developed in the fusion of Tin and Platinum. 12. New metal called Wodanium, discovered by Lampa- dius. 13. Singular Explosions of Fulminating Mercury and Fulminating Silver. 14. Potash in Sea-water. Analysis of the water of the Dead Sea. 16. New vege- MINERALOGY.-17. Mineralogical Map of Scotland. 18. Ame- rican Geological Society. 19. Mineralogical Society of St Petersburg. 20. Statue of Memnon. 21. Quartz-rock in North America. 22. Salt-mines of Villiczka. 23. Geo- gnostical situation of Lapis Lazuli. 24. Geognostical si- tuation of the Blue Copper of Chessy. 25. Primitive form of Chromate of Lead. 26. Primitive form of Cinna- ZOOLOGY.-27. Edinburgh College Museum. 28. Captain Carmichael on a curious fact respecting the Swallow. 29. Discovery of Human Skulls in the same formation as that 32. Detonating Mud in South America. 33. Meteoric phe- nomenon called the Lantern of Maracaybo. 34. Hot Springs of La Trinchera. 35. Excavations of Ants at Va- lencia. 36. Bottle thrown from the Alexander. 37. At- mospherical or Meteoric Dust. 38. Nicojack Cave, in which a river has its origin. 39. New Weights and Mea- 40. Preparation of Opium in India, ART XXXIX. Patents granted for Scotland since May 12. 428 THE EDINBURGH PHILOSOPHICAL JOURNAL. ART. I.-On a New Optical and Mineralogical structure, exhibited in certain specimens of Apophyllite and other minerals.* By DAVID BREWSTER, LL. D. F. R. S. Lond. and Edin. Communicated by the Author. ABOUT the end of the year 1816, I received from Major Petersen some fine crystals of the Apophyllite surcomposée of Haüy, from Fassa in the Tyrol. Upon exposing them to polarised light, I found that they had one axis of Double refraction; but I was surprised to observe, that the system of coloured rings, with which this axis was surrounded, was composed of unusual tints, the only colours of the first orders being bluishviolet and greenish-yellow, separated by a ring of white light. In order to ascertain the origin of these anomalous colours, I collected all the Faroe Apophyllites which could be procured, and upon subjecting them to a minute examination, I discovered the very extraordinary structure of this mineral, and was led to the results which it is the object of the present paper to describe. The Apophyllites from Faroe, crystallize in quadrangular prisms, with flat summits, having an almost imperceptible truncation upon the angles, and also in single and double four-sided pyramids, the planes of which correspond with the small truncations upon the prism, and form angles of 60" with those on the opposite side. The greater proportion of the quadrangular prisms have their planes highly polished, and very much stri This paper was read before the Royal Society of Edinburgh on the 1st of February 1819. ated; but there are others where the surface is less splendent, and where the crystal has the appearance of being more perfectly formed, as well as more compact and more transparent. Having cut off the slice, about the fiftieth of an inch thick, which formed the summit of a quadrangular prism, I found that it had only one axis of double refraction, and produced the same set of coloured rings, with the same anomalous tints, as the apophyllite from Fassa; but upon removing a second slice of the same size, it exhibited the beautiful appearance shewn in Fig. 1. This figure, resembling a tessellated pavement, is composed of four rectangles, RT, RV, VS, ST (Plate I. Fig. 1.), surrounded by a border MROVNSPT, and having at its centre a rectangle a b c d, with its sides opposite to the angles of the quadrangular prism. The tints depolarised by the four squares, were below the white of the first order, and that of the central rectangle was imperceptible; but in order to display the full beauty of the figure, and to ascertain the character of its tints, I placed the slice upon a plate of sulphate of lime, which polarised a yellow of the second order, so that the line MN coincided with the principal axis of that crystal. The brilliant yellow of the sulphate of lime was raised to a bright red, by its union with the tint of the squares RT, VS of the apophyllite, and was depressed to a fine blue by the opposite action of the tints in the squares RV and ST. The rectangle abcd remained yellow, and the border MONP had the same tints as the adjacent rectangles. Some of the pyramidal crystals are destitute of the tessellated structure, while others exhibit nearly the same phenomena as those which we have described; but owing to the truncation of the angles, the pattern has the appearance shewn in Fig. 2. where the border shewn in Fig. 1. is completely wanting. By taking a succession of slices from the pyramids, we see the structures shewn in Figures 3, 4, and 5, and we sometimes obtain the appearance represented in Fig. 6, where the central rectangle is wanting, and the tessela are bounded by irregular curves. If we place the slices of apophyllite upon a divided apparatus, and expose them to a polarised ray, it will be found, that at a perpendicular incidence, the first slice, and the rectangle abcd in subsequent slices, have no effect whatever in depolarising the incident light, but that they acquire it by inclining the polarised ray, and have therefore one axis and a circular system of rings round the axis of the prism. The rectangles RV, VT, on the other hand, will be found to depolarise a bluish white of the first order, when the lines RS or TV are parallel or perpendicular to the plane of primitive polarisation, but all their tints vanish when the lines MN, OP come into that plane, in the same manner as in plates of mica, and all other crystals with two axes. If we incline the apophyllite in the direction MN or OP, when RS or TN are in the plane of primitive polarisation, the tint will gradually diminish; and at an angle of about 17° 4′ with the axis of the prism, it will entirely vanish, as the refracted ray now passes through one of the poles of no-polarisation. By increasing the inclination still farther, the tints recommence, but with an opposite character, and the whole square MONP is covered with an uniform positive tint, the boundaries of the four large rectangles and the small central one being no longer seen. The cause of this singular result will be better understood from the following deductions, which the preceding experiments authorise. 1. The apophyllites from Fassa and Uto, have one axis of double refraction and polarisation, which is positive like that of quartz. 2. The central rectangle a bed of the tessellated apophyllite from Faroe, and the minute stripes of it formed by the lines monpm, ar, cs, bt, d v, have likewise one axis of double refrac tion. 3. The four rectangles RT, RV, ST, SV, have two axes of double refraction, the principal one of which is positive, and the inclination of the resultant axes is about 34o. 4. The plane of the resultant axes of the rectangles ST, RV, passes through their diagonals MN; but the same plane in the rectangles RV, ST passes through OP. Hence it follows, 5. That the four rectangles, even if they were not separated by the portions with one axis, would not form an uniform plate, and that RV is the same as RT turned round 90°; SV the same as RT turned round 180°; and ST the same as RT turned round 270°. 6. This singular construction has no resemblance to that of macled or hemitrope crystals, for the four rectangles are por |