turned to the river in order to halt for the night on its banks. We found here an agreeable and picturesque spot, vegetation rather rich, consisting mostly of cedar trees, of a size far infe rior to the European cedar. The banks here were less elevated, and afford an easy passage, although large rocks abound in the river; and upon the left bank sand-dunes are still seen. At this point we met with many traces of the elephant, zebra, the deer, the fox, the monkey, and the lion. The direction of the stream is N. West. We resumed the march on the following day, with no expectation of replenishing an almost exhausted stock of provisions. We halted at 9 in the morning, and after disposing of the remainder of our provisions, were on the point of turning back, when very luckily one of our soldiers killed a young elephant that accompanied by its dam had ventured within range of our guns. Soon after we resumed our march. The general appear ance of the region through which we were advancing was the same, with this exception, that the vegetation seemed to be more fully developed, and the traces of the various animals, especially the elephant, became more numerous. This led us to believe that farther in the interior, great herds of elephants frequent the banks of the Cunene, which at certain seasons of the year, advance towards the mouth of the river. From the source of the stream to the point which we were able to attain, a distance of about 21 miles, we fell in with eight elephants, which all withdrew into the interior. Up to this point the Cunene presents no points of any importance; its course is winding, the bed of the river narrow and obstructed by waterfalls, and hence not navigable. For even if these were to be removed, (which is not impossible,) yet the mouth of the river could not be cleared; for the current of the river, removing the sand-dunes on the left bank constantly deposits them near the mouth where the water is shallow and the current not so strong. Whether the Cunene be navigable at any point, we are as little able to say, as at how great a distance the tribes living on its banks kept themselves from us. We discovered a mountain range of considerable height, running in a direction from north to south; but it was impossible for us to cross this range, since we were in no respect furnished with the necessary means. Our mission being quite a different one and already accomplished, we commenced our journey homeward on the 16th of November, and arrived at the Great Fish Bay on the following morning at 10 o'clock. The extent of our whole journey on foot being about 30 miles. The result of the expedition is already apparent. Many of the inhabitants of Mossamedes, engaged in the trade of the desert, are preparing themselves for an excursion by land to the banks of the Cunene. If a friendly intercourse with the people of this region be kept up, the colony will here find a new source of trade and wealth. This would result in leading that nation to carry on a direct trade with Mossamedes, after the example of the people of Gamba, Huilla, Jau, Humputa, Quillengues, Humbe, Kamba, Mulonde, and other places. Yale College Library, April, 1859. D. C. G. ART. XLII.-On a new Sulphid of Copper and Lead; by FREDERICK FIELD. IN the 'Mina Grande' near Coquimbo, Chili, there exists a mineral containing sulphur, lead and copper, in certain proportions which render it highly interesting. From the same mine have been obtained the following ores of lead: vanadiate of lead, vanadiate of lead and copper, arseno-phosphate of lead, sulphate of copper and lead, and carbonate and sulphid of lead, besides an intimate mixture of sulphid and sulphate of lead, the former mineral evidently undergoing gradual oxydation. The double sulphid of copper and lead has the following properties. Sp. gr. 6:10. H. from 25 to 3. Massive. When broken, a slight conchoidal fracture, having a deep indigo-blue color, quickly tarnishing on exposure to the atmosphere. Immediately associated with carbonate of lead and carbonate of copper. The pure mineral is violently acted upon by nitric acid, with the formation of sulphate of lead and liberation of free sulphur. 100 parts yielded Copper, 53.63 28.25 17.00 98.88 corresponding to 3Cu, S, PbS, which requires Cu 53.33, Pb28-88, S 17.77. The only other simple combination of sulphid of copper and lead with which I am acquainted is the cupro-plumbite of Plattner, (also from Chili,) which is a compound of Cu, S, 2Pb S. I have proposed the name Alisonite for this mineral, in honor of R. E. Alison, who has spent many years in developing the mineral wealth of Chili. Guayacan, Coquimbo, Jan. 29, 1859. APPENDIX. In a letter to one of the editors of the same date, Mr. Field observes, that the mineral described by him under the name of Guayacanite (this volume, p. 52), he has found to be the rare species Enargite. ART. XLIII.—An Abstract of Prof. von Kobell's Stauroscopic Observations; by OGDEN N. ROOD, Professor of Chemistry in Troy University. THE following pages contain a brief abstract of Prof. von Kobell's observations with the stauroscope, an optical instrument lately invented by him and designed to be used in optico-crystallographical researches.* In a previous number of this Journal+ the instrument was described and figured; the annexed diagram will therefore be suf ficient to point out its optical arrangement. P is a plate of glass which reflects polarized light toward the E eye at E, S is the stage-plate or engraved square, C the crystal under investigation, R a plate of calc spar cut at right angles to its optic axis, and T is the analyzing tourmaline. During the ex R T 1. periments the stage-plate S with the crystal is revolved about the axis EP, the rest remains stationary. I have found it much better to use two Nicol's prisms instead of the glass plate and the tourmaline, and in my own experiments at the end of this article they were employed exclusively. The plate of calc spar being in its proper position, the tourmaline is turned so as to darken the field, and upon looking through the instrument the usual black cross is seen, of which we shall afterwards speak, surrounded with its concentric colored rings. The dark field which would be seen without the plate of cale spar is more sharply defined by the cross. When the third cylinder is put in, its slider fitted to the second, and the divided circle turned around to zero, then two sides of the engraved square coincide in position with the axis of the tourmaline. If it be wished to determine the directions (or planes) in which the polarized rays of a double refracting crystal vibrate with regard to the edges of the observed crystal plane, the crystal is to be fastened with wax on the engraved plate over its opening, and turned till one of its sides is parallel with one of the sides of the engraved square, the cylinder with the crystal is then slid in, and the graduated circle turned to 0. See von Kobell's "Mineralogie," 2nd edit. 1858, p. 47. If the cross is seen unchanged in its position then the polarized rays of the crystal vibrate in the direction of the side of its plane and at right angles to it, but if no cross should appear, or if it should be changed in its position, it is a proof that the rays do not vibrate in the direction of the edge of the crystal plane under observation, and it is necessary to turn the cylinder to which the crystal is attached a certain fixed number of degrees till this happens and the cross again appears in its upright normal position; the angle is read off by means of the vernier. In this manner it is possible to obtain through the stauroscope certain characteristic optical distinctions for the different crystalline systems, by which they often may be determined when other means fail. I. System of simply refracting crystals. MONOMETRIC SYSTEM. Monometric crystals show, in every position in which they can be put on the stage, the cross normal; however the stage may be turned it remains unchanged. Examples: Rock salt, alum, spinel, fluor. Amorphous pieces behave in the same manner. II. Systems of doubly refracting crystals. All doubly refracting crystals show in certain directions the cross inclined, or by revolving them they extinguish the normal cross; it is only in the directions of their optic axes that they behave to a certain extent like monometric crystals. Systems with one optic axis. 1. DIMETRIC SYSTEM. (1.) Seen through a plane of the quadratic pyramid the cross arranges itself according to the verticals of the triangle or at right angles to each of its sides. (2.) Through the prismatic faces the cross has the position of the principal axis. (3.) Through the basal plane the cross appears normal and remains unchanged when the crystal is revolved. Examples: Apophyllite, idocrase, zircon, scapolite. 2. HEXAGONAL SYSTEM. (1.) Through a plane of the hexagonal pyramid the cross stands in the directions of the verticals of the triangle or at right angles to each of its sides. (2.) Through the sides of the rhombohedron the cross arranges itself in the directions of the diagonals. (3.) Through the faces of the scalenohedron the cross arranges itself according to the lines of altitude of the sides of its holohedral dihexagonal pyramid, or at right angles to the sides of its horizontal twelve-sided transverse section. (4.) Through all the prismatic sides the cross is seen normal in the direction of the principal axis. (5.) Through the basal plane the cross is seen normal and unchanged by the revolution of the crystal. Examples: Apatite, quartz, calcite, chabazite, emerald. Systems with two optic axes. In these systems there occur no planes through which the nor mal cross remains unchanged during the revolution of the crystal. 3. TRIMETRIC SYSTEM. (1.) Seen through a plane of the rhombic pyramid the cross makes three angles with the three sides, corresponding to the inequality of the sides of the triangle. (2.) Through the prismatic faces and also through the macroand brachy-diagonal planes the cross is in the direction of the principal axis, also through the domes it is in the direction of the dome edge. (3.) Through the basal plane when it is rhombic the cross stands in the direction of the diagonals, when it is rectangular in the direction of its sides. By revolving the crystal the cross becomes pale or is altered by colors. Examples: Heavy spar, topaz, sulphate of magnesia, aragonite, chrysolite. 4. CLINO-RHOMBIC OR MONOCLINIC SYSTEM, (1.) Through the lateral planes of the oblique rhombic prism the cross is inclined to the principal axis; also through the planes of the clinodome it is inclined to the dome-edge. The angle through which it is necessary to turn is the same for like planes, and the crosses are turned towards or away from the clinodiagonal chief section to the right or left with equal angles, when seen respectively through the back or front sides of the crystal. (2.) Through the orthodiagonal plane the cross is normal in the direction of the principal axis. (3.) Through the clinodiagonal plane the cross is inclined to the principal axis. (4.) Through the basal plane of the rhombic prism the cross stands according to the diagonals. Examples: Diopside, selenite, orthoclase, epidote, borax. |