On Crystallography, 27^ 



fraction. relative to a third decrement which is mixed. 

 Ek. Identical gray c<^ppcr. 



<?. Isonomous, i.e. equality of laws, when the parts visible 

 which indicate the decrements on the edges being 

 equal, those which express the decrements on the 

 angles are equal also. Ex. Isonomous sulphated copper. 



p. Mixedy when the form results from a single mixed de- 

 crement. Ex. Mixed telesia. 



q. Paniogenofis, i. e. deriving its origin from all the partSy 

 when each ridge and each solid angle undergoes a de- 

 crement. Ex. Pantogenous sulphated barytes, 



r. Bifcrous, i. c. tvhivh carries twice^ when every ridge and 

 every solid angle undergoes two decrements. Ex. Bi- 

 ferous gray copper. 



s. Sw rounded, (entour^) when the decrements take place 

 on all the ridges and on all the solid angles around the 

 base of a prismatic nucleus. Ex. Surrounded sulphated 

 barytes. ' 



t. Opposite, when a decrement is made by one row, aiid 

 another is intermediary. Ex. Opposite oxidated tin. 



?/. Synoptic, when the laws of decrement present as it were 

 the picture of those which take place with respect to 

 the whole of the other crystals, or at least with respect 

 to the greatest part. Ex Synoptic feldspar. 



X. Retrograde, is a variety of carbonated lime, the expression 

 of which contains two mixed decrements, which are 

 such that the faces resulting from them seem to retro- 

 grade, by throwing'ihemselves backward, on the side 

 • of the axis opposite to that which looks towards the 

 face on which' ihey originate. 



y. Ascending, when all the laws of decrement have an 

 ascending course, setting out from the angles or lower 

 edges of a rhomboidal nucleus. Ex. Ascending car- 

 bonated lime. 



S. Secondary forms considered relatively to the geo- 

 metrical properties which they present. 

 The crystal is called, 

 a. Isogonous, i. e. equality of angles, when the faces which 

 are on parts differently situated form equal angles be- 

 tween each other. Ex. Isogonous cymophane" 

 h, Anamorphic, \ . g . form turned upside down, when we 

 cannot give it the position most natural to it, without 

 that of the nucleus being as it were turned upside down. 

 Ex. Anamorphic stilbite. 

 c. Wiombiferousy when certain E^cet^ are true rhombuses, 

 S 2 although. 



