positive sphenoid. Crystals were also observed intermediate between figs. 2 and 1 with the planes of the negative sphenoid in different degrees of development. The crystals of the variety represented by fig. 2 contained a small amount of rubidium; but this isomorphous admixture did not perceptibly alter the angles. We measured on three different crystals These crystals were very perfect and comparatively large, measuring about 7 millimeters long by 5 millimeters wide in the direction of the brachy diagonal. As with the first variety, no accurate measurements could be obtained of the angles between the prismatic planes. The second type of crystals is represented by the figures 3 and 4. On these forms we have the planes of a left-handed sphenoid, 43, which are not found on crystals of the first type, and are here so largely developed as to give a very different character to the crystal. Planes of the corresponding positive sphenoid were not discovered, although a large number of crystals were examined. These planes were very dull and rough, even on the smallest crystals, and could not therefore be deter mined with absolute precision. A reflected image was obtained by attaching to them small plates of mica, and the angles were thus approximatively measured, but the results cannot be relied upon within two or three degrees. The values obtained No other probable parameters of these planes would even approximatively satisfy these values. The crystals represented by fig. 3 differ materially from those represented by fig. 4, and were obtained by a different crystallization. All of the first have the planes +1, which could not be detected on those of the last. On three separate crystals of the form fig. 3, the angle +1 on I measured 139° 15', the same as on the crystals of the first type. It is evident, then, from this examination that the bitartrate of cæsia forms two different types of crystals, which present respectively a right-handed and left-handed hemihedrism. Either of these hemihedral forms may appear without the other, as in figs. 2 and 4, or they may be united on the same crystal, as in fig. 3. It would be interesting to examine in this connection the optical properties of the salt, but we had not sufficient material for the purpose. The crystals were all proved by spectroscopic examination to be pure bitartrate of cæsia, with the exception of those like fig. 2, which, as already stated, contained a small amount of rubidium. Nothing is known in regard to the conditions of the crystallization, which would to any degree explain the formation of the two different types of forms. The most obvious hypothesis is that they are connected in some way with the two opposite modifications of tartaric acid; but there is no evidence that any other than the ordinary variety of tartaric acid was used in the preparation of the salt. 2. Bitartrate of Rubidia, HO, RыO, C,H,O,..-This salt resembles very closely the last, with which it is isomorphous. The crystals examined were all similar in character, about 5 millimeters long by 2 millimeters wide, and very perfect. They belong to the trimetric system and have the axial relations, a b c 0·695: 1: 0.726 5. The planes observed, with the exception of -1, are represented on fig. 5. They are the same as on the last, with the exception of the negative sphenoid -43. Of this no trace could be discovered. The planes -1, moreover, were at best very small and generally wholly absent. The angles measured or calculated are as follows: AM. JOUR. SCI.-SECOND SERIES, VOL. XXXVII, No. 109.-JAN., 1864. Four different crystals were measured, and the angles on all closely agreed with the exception of the angles between the pris matic planes. To these the same remarks apply as to those of the crystals of the bitartrate of cæsia. As is shown by the figure, the planes li are more largely developed on the crystals of the rubidium than those of the cæsium salt, and in this as well as in the other figures, we have endeavored to preserve as nearly as possible the general habitus of the crystals, as well as the relative dimensions of their planes. The cleavage of the crystals of the bitartrate of rubidia is in all respects similar to that of the cæsium salt, and the same is true of the crystals formed by an isomorphous mixture of the two substances. Moreover, the planes i and are similarly i striated on both. 3. Bitartrate of Potassa.-We add for the sake of comparison the elements of the crystalline form of the ordinary bitartrate of potassa as determined by Schabus ("Rammelsberg's Krystallographische Chemie," page 304). His results, reduced to the system of notation used in this article, are a:b:c=0.7372:10-7115, Z=103° 38'. X=100° 20', For the most part, the same planes occur as on the crystals above described, but the planes of the brachydome are more numerous and more developed. Moreover, the planes i instead of being striated vertically, as on these crystals, are striated horizontally, and corresponding to this striation the most perfect cleavage is parallel to the basal section. Cleavages can also be obtained parallel to and , but they are less perfect, the last being the most difficult of the three. It will be remembered that the crystals of the bitartrates of casia and rubidia could not be cleaved parallel to the horizontal section, and hence, although the dimensions of the form are not widely different, the difference of structure is so great that the potash salt can hardly be regarded as isomorphous with the other two. The crystals described in this article were prepared, in the Sheffield Laboratory of Yale College, by Mr. O. D. Allen, from the Hebron lepidolite, and we are indebted to his kindness for submitting them to our examination. They have an additional interest from the fact that in his hands they have furnished the means of separating perfectly the two new metals, and of determining with great accuracy the chemical equivalent of cæsium. Cambridge, November 25th, 1863. ART. IX.-Geographical Notices. No. XIX. SPEKE AND GRANT'S EXPLORATION OF THE SOURCES OF THE NILE. THE great event of the year 1862, in geographical exploration, has been the reported discovery of the sources of the Nile by the perseverance and boldness of two English officers, Capt. J. H. Speke, and his associate Capt. J. A. Grant. A telegraphic despatch from Alexandria to London brought, in May, the brief announcement, "The Nile is settled;" shortly afterward the journal of the travellers was communicated to the Royal Geographical Society, and finally, on the 17th of June last, the explorers themselves arrived at Southampton. A meeting of the Society just mentioned, under whose auspices the expedition had been sent out, was immediately called, and in it Capt. Speke made a statement full of interesting particulars in regard to the route he had followed and the discoveries he had made. Those of our readers who have followed the progress of African exploration will remember that in 1858, Capt. Speke (then travelling in company with Capt. Burton) discovered the head of a great, fresh-water lake lying close on 3° south lat., and at an elevation of about 4000 feet above the sea line, which he at once conjectured, from its size and position, as well as from all which the natives told him of its extent, to be a principal source of the river Nile. This lake was called by the natives Nyanza, a term signifying Water, Lake, Pond, or River, to which the English discoverer added the name of his sovereign, christening it Victoria Nyanza. Being prevented at that time from putting his conjecture to the proof, Capt. Speke returned to England, and with the patronage of the London Geographical Society and the British Government, went forth in 1860, on a new expedition, having for his chief object the determination of this specific question. Reaching the coast of East Africa about the first of October, 1860, Messrs. Speke and Grant made their way to the southern point of the Nyanza, and thence going northward they traced one of the principal affluents of the Nile from its source in the lake to its union with the great river itself. This result has been heralded everywhere, in general terms, but having received Capt. Speke's own Report of the journey we prefer to place its details on record here. Their sagacity, perseverance, bravery and success elicit universal commendation. We understand that a volume may be expected from the explorers at an carly day, from the press of Wm. Blackwood, Edinburgh. ' v. Proceedings Roy. Geog. Soc., Lond., vii, 212-217. For an illustration of the relations of the Victoria Nyanza to Lake Tanganika, and the River Shire, the reader may consult to advantage a map by Mr. Ernest Sandoz in the American Geographical Society's Proceedings, October, 1862. Capt. Speke's narrative begins with reminding his hearers that his observations are the results of two visits to the region, and that he has not followed the river from head to foot, but has tracked it down, occasionally touching upon it. His statement blends native information with his own experiences. He then continues,— "After returning to Unyanyembi (the old point) 3° S. of the lake, in 1861, I struck upon a new route, which I imagined, from the unsophisticated depositions of the ivory merchants, would lead me to a creek on the westerly flank of the Nyanza, situated on the southern boundary of Karagwé. Geographical definitions were here again found wanting, for, instead of the creek to the great lake appearing, a new lake was found, called Luero-lo-Urigi, or White Lake of Urigi, which appeared to have formerly contained a considerable amount of water, but is now fast drying up. Its head lies in Urundi, and, circling round the south and east flanks of Karagwé, in form a mountain valley, is subsequently drained by the Kitangulé River into the Nyanza, but not in sufficient quantity to make any sensible impression on the perennial contents of the Nyanza basin. It is to the west and south of Karagwé that the lake receives its greatest terrestrial supply of water, through the medium of the Kitangulé River, which, in draining the aforesaid Luero-lo-Urigi, drains off the superfluous waters of many minor lakes, as the Akenyara in Urundi; the Luchuru, which is the second of a chain including the Akenyara; the Ingezi and Karagimé; and the little Winandermere, which in Karagwe lies below the capital on its southeastern corner. None of these lakes are large-mere puddles in comparison to the great Victoria Nyanza; but still the Kitangulé, after receiving all their contributions, is a noble river, low sunk like a huge canal, about 80 yards across, with a velocity of about 4 miles an hour, which appears equal to the Nile itself, as soon as it issues from the lake by the Ripon Falls. The question naturally suggests itself, What forms these lakes?-whence originate their waters? It is simply this: the Mountains of the Moon, in which they lie, encircling the northern end and the Tanganyika Lake, are exposed to the influences of the rainy zone, where I observed, in 1862, no less than 238 days out of the year were more or less wet ones. Mashondé, in the upper portion of Uganda, is the first place where, in this second expedition, I obtained a view of the Victoria Lake, called in these more northern countries Luero-White (lo-of) Luta (dead) Nzigé (locust), in consequence of the reputed fact that flights of locusts, in endeavoring to cross these waters, have dropped' down from fatigue, unable to accomplish such an extended journey on wing, and, perishing in the lake, have been found dead in dense masses by the boatmen. But, like the word Nyanza, it is also applied to the Nile and its tributaries, thus confounding all inquiry. This is the explorer's greatest difficulty in endeavoring to put together the information which he hears, though it may be overcome by close questioning, even |