4 Lange, Some Remarkable Steel Crystals. 



octahedral envelopes, which he says recall exactly the 

 beautiful steel crystal of Professor Tschernoff. 



The late Dr. Hermann Wedding also refers to the 

 "skeleton " structure saying that " in commercially pure 

 "iron the crystals show the form of an incomplete regular 

 " octahedron, that is to say, the external form corresponds 

 " to the octahedron, but the mass of the crystal is not filled 

 " up, but is replaced by beams {Balkeii) which run in a 

 " direction parallel to the octahedron axes, and conse- 

 " quently correspond to the position of the belonging cube 

 "faces. Such " beams " have, in the rule, side " beams " 

 " standing at right angles to the main beams, these also 

 " again have often perpendicular beams of the third 

 " degree, so that the whole is only the skeleton of an 

 " octahedron, and has the external form of a pine-tree, or 

 " as the mineralogist would say, receives a knitted or 

 " net-work (gestrkkte) form." 



Messrs. Vickers Ltd. kindly placed at my disposal for 

 microscopical examination the end portion of one of the 

 shorter crystals. This was cut into two halves longi- 

 tudinally, bisecting two opposite angles. The two cut 

 surfaces of one of these halves were then ground up to an 

 exact right angle with each other, and then polished and 

 etched with picric acid. 



On examining the section with the unaided eye, a very 

 striking pattern of remarkable geometrical s}'mmetry was 

 revealed, particularly on allowing the light to fall on the 

 section from an angle. This I photographed direct, and 

 then enlarged to twice the linear dimensions. This photo- 

 graph is faithfully reproduced in Fig. 2, Plate II., without 

 the smallest retouching in any way, and speaks for itself as 

 regards the regularity of the pattern. A line corresponding 

 to the main longitudinal axis is plainly seen, and this is 

 intersected at right angles by a series of parallel lines 



