654 Journal of Applied Microscopy. 



zone of 110, 130, 010, 100. They are highly pleochroic, deep violet for vibra- 

 tions parallel the length, and violet-red at right angles, and with convergent light 

 both axes show in 100. 



Axial ratio, a .- ^ .- ^=0.9034 : 1 : 1.2036 /i=117° 13'. 



A. J. M. 



Bourgeois Le'on.-Sur un chlorate basique de Manner of making described and 

 cuivre cristallise. Bull. Soc. Min., 21 : 170, crystallographic and optical examina- 

 ^ ■ tion recorded. 



Consists of very small, green, orthorhombic tablets, resembling gerhardtite 

 and isomorphous with it. Insoluble in water, but easily soluble in acids. G.^ 

 8.55. Analysis yields formula, 4 CuO. CI2O5 -\- 3 HgO, or (CI 03)2 Cu -\- 



3Cu(0 H)2. L.McI. L. 



V. Qoldschmidt. Ueber einen Krystallmodel- Prefacing a description of an appara- 

 lirapparat. Zeit f. Kryst, 31 : 223, 1899. ^^^ f^j. cutting crystal models. Prof. 



Goldschmidt points out that the use of models in the study of crystals may 

 be divided into three stages: 



1. Elementary instruction, in which models are more considered than 

 actual crystals, the latter being employed only when they are simple and 

 approximate the ideal or model form, such as octahedrons of magnetite, cubes 

 of pyrite or dodecahedrons of garnet. 



2. Higher instruction, in which the student commences to realize that in 

 nature there are no perfect cubes or octahedrons, that crystals are usually small, 

 partially formed, generally show combinations, and that one crystal in its form- 

 ation often disturbs the formation of another. The student now measures, 

 draws and calculates for himself, and gradually reaUzes the beauty and wonder- 

 ful regularity of the crystals, and the models appear crude and incorrect and 

 relatively valueless in comparison with projections. 



3. A stage which might be called that of the investigator, in which models 

 again are valued, which show directly what is being observed and what has 



been seen on similar material. Such models are not to be purchased. 



The new apparatus is based upon the principle of the two-circle goniometer 

 in which the position of any face is determined by the direction of a ray normal 

 to the face. Two angles cp and p, which are recorded for all known forms of 

 natural crystals, determine the directmi of this ray with respect to a pole and a 

 first meridian, and to locate the face it is only necessary to know the distance to 

 the center. 



A vertical circle {cp circle) and a horizontal circle (p circle) graduated to one 

 degree are used. The axis of the <p circle carries a fragment of, say, gypsum or 

 soapstone. A movable knife is attached to the horizontal circle at the angle 

 given hy (p p and cuts away from the block layers parallel to the desired face 

 until the desired central distance is attained. The largest faces are cut first. 



The central distances, the author claims, will be in essentially the same ratio 

 in the model and the crystal if the cutting is continued until to the eye the shapes 

 of the faces are essentially those of the crystal. 



These central distances determine the habit of the crj^stal and, as is known, 



