: 



AUGITI:. 



AUK. 



.11* 



appearance ; while on charcoal it readily forma a green opaque glass, 

 as U alo the oaw when heated with borax. 



The aalt of phosphorus does not apparently decompose it, but the 

 mineral at first become* rounded on the edge*, and may at length bo 

 entirely fused. 



The structure also deserves particular attention, the cleavage-plane* 

 in Jlyperttkau being perfect, both in the direction of the faces r 

 and M, the latter of which are obtained in DiaUagt with very great 

 difficulty. 



We have now described the various species generally considered as 

 comprehended within the genus Auyite or Pyroxene; but Professor 

 Oustave Rose has endeavoured to prove the necessity of uniting A uyite 

 and Hurnblmde (Pynurtne and AmpkiboU) into one genus. His argu- 

 ments fur this union are the following : He first shows that the two 

 prisms of Auyite and Hornblende, however different in appearance, 

 admit of being derived the one from the other, according to the laws 

 observed to connect the crystallographic forms of varieties of the same 



genun in other 

 mincntls. To show 

 this, let the accom- 

 panying parallelo- 

 gram, whose semi- 

 diagoualn are a and 

 b, represent the 

 horizontal section 

 of the prism of 

 .!'//'>; since the 

 whole angle of this 

 prism at A is 87 6', 

 o is the tangent of 

 an angle of 43 33' ; 

 if this tangent be doubled, the corresponding angle will be found to 

 be 62 15' 25", the double giving 124 30' 50", an angle agreeing most 

 closely with 124 31', the angle obtained by Mitscherlich in a species 

 of Hornblende when measured by Wollaston's reflecting goniometer. 

 The larger parallelogram, therefore, formed by doubling the diagonal 4, 

 is the horizontal section of the prism of Hornblende. 



A similar relation is also approximately true for the inclination of 

 the faces in Augiie and r in Hornblende; for if the angle 120 57' of 

 A ugite be halved, and its tangent doubled, the corresponding angle is 

 74 11' 21", and by doubling this we obtain 148 22' 42", not much 

 differing from 148 25', as found between r in Hornblende of Vesuvius 

 by Rose. 



His argument drawn from the chemical constitution of these 

 minerals is by no means so satisfactory; for though in Hornblende we 

 find a series of bisilicatoa of the same bases, and as it were running 

 parallel with those already described as Augittt, the circumstance 

 observed by Bonsdorff, that all the varieties of Hornblende contain 

 fluorine, while Oustave Rose has been unable to detect that element 

 in A uyite, weakens the connection between these minerals, and renders 

 the determination of what part the fluorine acts in their constitution 

 a most desirable object. Our ignorance on this point, however, and 

 the difficulty of determining what is the action of the alumina, which 

 occurs in considerable quantity in some Hornblende*, prevent us from 

 forming any opinion from the results of chemical analysis. 



The observations of Rose, however, on the Greenstone of the 

 Uralian Mountains, tend to prove the existence of that connection 

 between the forms of Auyite and Hornblende which is essential to 

 their constituting one genus, in a more satisfactory manner than any 

 remark hitherto made. He discovered in a soft grayish Greenstone, 

 near the village of Hostowaja, which is situated north of Katharinen- 

 burg, and on the road to Newiansk, and also at the gold-washings of 

 Cavellinski, near Miask, in a Greenstone somewhat harder and darker 

 than the former, imbedded crystals, having the form of .1 ./''.. 1ml 

 not its cleavage planes, these last being found to coincide with those 

 of Hornblende. This mineral was therefore either Hornblende in the 

 funn of A ugite, or A ugite with the cleavage planes of Hornblende. 



At the village of Muldakiijcwsk, near Miask, he discovered still 

 more interesting crystals embedded in a Greenstone similar to that 

 last described. They were abundant, and possessed the form of A ugite : 

 the smaller crystals had cleavage-planes parallel to the sides of the 

 prism of Hornblende, and were similar in their appearance and colour 

 to those obtained from Cnvellinaki. The larger crystals, however, 

 possessed a kernel of a grass-green colour, and of a lighter tint am! 

 greater lustre than the exterior. This kernel differed from the darker 

 exterior portion of the .crystal, the latter giving the cleavage ol 

 Hornblende, while the former presented those of Avyite, with faces 

 sufficiently bright and perfectto admit of measurement by the reflect- 

 ing goniometer. 



The observations of MiUcherlich and Berthier on the formation ol 

 Auyite as an artificial product, are so interesting in themselves and 

 throw so much light on the nature of Auyite in general, and on those 

 crystals we have just described, for which Rose proposes the name ol 

 l.'ralilf, that we cannot omit to notice them hi this place. Mitscher- 

 lich has observed that at many foundries in Sweden and Germany the 

 KOorUp po HBsscd tin- f,. rin, H'riictnr.-.;. ml rh. 'Miic^l cnm]Hi!<itinii of certain 

 minerals found in natnn . From ho has obtained upward 



of forty varieties; and among these specimen! possessing the funn 



and structure of Auyite are frequently found, whereas Hornblende has 

 never been discovered. Guided by these observations, a mixture of 

 silica, lime, and magnesia, in the proportion indicated by the formula 

 of Dioptide, given below, was submitted to fusion in the porcelain-ovens 

 ){ Sevres, near Paris. On examination, the mass was found to have 

 been completely fused: it possessed cleavage-planes corresponding 

 with those of Augiie, and a hollow formed in the centre from the con- 

 traction in cooling contained crystals of the form of fy. 1. By these 

 processes they failed in obtaining crystals either of the form or struc- 

 ture of Hornblende. 



Professor O. Rose, in accounting for this production of A ugite to 

 the exclusion of Hornblende, was led to consider that it was not the 

 absence of the fluorine, or any error in tlje proportion of the elements, 

 which prevented the production of J/ornblmile, but that it was the 

 effect of the rapid cooling. Tlii.- he fully confirmed by the following 

 experiments : A light-green variety of Hornblende, the 8traJiltlein of 

 the Germans, from Zillerthal in the Tyrol, was submitted in a plati- 

 num crucible to the heat of a porcelain oven. It was completely 

 Fused, and in cooling had formed fibrous tufts of dark crystals, wUoR 

 bowever admitted of measurement by Wollaston's goniometer, w lu-u 

 the angles were found to correspond with those ufAuyilr. A specimen 

 of IKoptide, of the same locality, was also fused ; it cooled into a dark 

 mass, but regained its former structure. 



We may therefore consider it to be demonstrated that A uyitt is 

 formed whenever the process of cooling, and consequently of 1 1 

 lisation, is rapid ; and Hornblende, when it is conducted more slowly. 

 Many circumstances confirm this view : the I'ralitet of Rose appear 

 to be its natural consequence : for as by the laws of caloric we know 

 that the quantity of heat lost during equal portions of time varies 

 with the temperature, the exterior portions of the crystal from tins 

 cause alone must have crystallised under a more gradual loss of heat 

 than the interior, while at the same time the temperature would 1) 

 maintained by the specific heat given out by the parts first consolidated. 

 The general localities of Auyite and Hornblende, and the minerals with 

 whieh they are found associated, afford another argument in favour 

 of this supposition; for Hornblende is usually met with in S;. 

 Trachyte, and Lava, accompanied by Quartz, Felspar, Albite, Ac., 

 minerals which decidedly require a slow process of cooling (\ their 

 formation; on the contrary, Auyite occurs in Basalt anil Lava with 

 tiliriiif, which MitMcherlich has recognised in the scoritB of various 

 foundries, and which is therefore formed by a process of rapid cooling. 

 We are thus able to account for H. von Buch's remark in his observa- 

 tions on volcanoes, that those Lavas which contain Felspar have 

 J/'iniltlrmlf, but no Auyite. 



Induced by these circumstances Kn-e. in a tabular view of the 

 minerals which he has added to hi* ' Klementi of Crystallography,' 

 published at Berlin in 1833, has united into one genus the following 



1. Dioptide . . 



2. Sahlite 



8. Hedenbergite . 



. <'a Si- + Mg Si*. 



Ca Si' + ^H Si*. 

 . . Ca Si= + Fe Si*. 



4. Btualtic Augite . . Ca, Mg, Fe, Al, Si. 



5. Rolhbrauntlemerz . Mil Si*. 



6. Acmite , . . 3 Na Si 3 + 2 Pe Si. 



-. IHaUage . , 



8. Bronzite . . 



9. Hypenthene . 



in. r'nilitf . . 



11. Tremolite . , 



12. Antophyllite. 



l: 1 Xtraklttei*. 



, .Mg &*+* Si-. 



..MgSK 

 . Mg Si 5 + Fe Si*. 



, ". Ca Si' + 3 Mg Si . 



. . Fe Si 3 + 9 Mg Si-'. 



, . Ca, Mg, Fe, Al, Si. 



1 I. fiataltic Hornblende Ca, Mg, Fe, Al, Si. 



A 1"K. tli.- i '!M! IK in name for certain sea-birds of the family .\lratlir, 

 including species of the sub-genera Atca, Pratercula, Hergului, and 

 PkaUrii. 



Alfa. [At.CA.] 



The true Auks, though they are strictly oceanic birds, scarcely ever 

 leaving the water except for the purposes of reproduction, will 

 times proceed swiftly though awkwardly on foot \\li.n pur-n.-.l ..n 



I iiul. They breed in large companies, in cuvenis .-UK! i ly rlill-, 



laying only one disproportionately large egg. Their f.....!. whi. h they 

 obtain by diving (an operation in which they are in 

 by their wings as well as by their feet), consists of small li.sheR, 

 crustaceans, and other marine animals. The young are said to be fed 

 fr. mi the crops of their parents, not only before they are able t< > 

 the place of their birth, but also for some time afterwards. 



The genus A lea, as it is reduced by modern ornithologi 

 but two species. The first of these, thu Great Auk (Al 

 l.inna'ii ), M n-miirkalile I'ortlie imperl'eet <le\i lopmunt of its win^n. 

 It seldom leaves the Arctic Circle and the regions bordering on it .and 



