THE PRODROMUS 245 



glistening planes resembling the truncated sides of triangular 

 pyramids. 



It seemed to me worthy of notice that by truncating a cube 

 at the very extremity the entire number of planes in the third 

 kind of angular bodies of iron can be shown; for it has six 

 pentagonal planes which coincide with the planes of the cube, 

 and which, at the four angles,^ bisect the individual sides of the 

 cube's planes. All the remaining planes are found at the cube's 

 angles when they are truncated in a certain way. 



In the angular bodies of iron there is also another thing 

 equally surprising. In the second class of angular bodies of 

 iron the terminal planes, which are striated and five-sided, are in 

 process of time changed to three sides, while intermediate planes, 

 which are three-sided and brilliant, pass into five-sided with two 

 right angles adjacent to each other.^ Between two five-sided 

 planes, however, where their right angles are adjacent, a pair of 

 triangles, or two three-sided planes, are formed, likewise brilliant, 

 whose bases coincide with the perpendicular side of the five- 

 sided planes ; so that the second class of iron is thus changed 

 into the third. 



That in this same way a body of twenty-four planes is formed 

 from a body of twelve, I am convinced for the following 

 p. 48. reasons : (i) Because in the same mass of iron bodies almost 

 all the thinner bodies have only twelve planes, while the thicker 

 ones have twenty-four. (2) Because in certain bodies of twelve 

 planes are seen the beginnings of triangular planes which are 

 accessory and which, if continued, form a body of twenty-four 

 planes. 



In triangular planes I have sometimes noticed a smoothness 

 so perfect that not the slightest unevenness was apparent to the 

 eye, — something which it has never yet been my lot to see in 

 any crystal.^ In other instances I have seen smaller curved 

 planes piled above larger, of which the higher were, for the 

 most part, nearest the triangular apex, so that one may there- 

 fore question whether the five-sided planes are not formed by 



1 The polyhedral angles. Steno is apparently referring to the relation of the rhombohe- 

 dron to the cube. 



2 Steno evidently thought that the various modifications of hematite resulted from an 

 evolution in time of new crystal forms. 



3 Quartz or rock crystal. 



