lis Mi\ Brooke on the [Aug. 



independent rather than as related forms, and the mind was 

 thus led away from the consideration of their relations to each 

 other, rather than assisted in comprehending them. 



It is probable that the study of crystals will be much assisted 

 by a general series of forms, serving as a type, with which 

 all the crystals of different substances might be readily com- 

 pared. This series I have attempted to supply in the volume 

 already alluded to, which contains tables of all the modifica- 

 tions of which the simple crystalline forms are susceptible. 



The letters placed on the figures which accompany these 

 remarks correspond with those used in the tables here refer- 

 red to ; and by means of these, the reader may trace the 

 relations of all the planes on these figures, to the simple primary 

 form from which they are supposed theoretically to be derived. 

 I have, therefore, omitted, in most instances, to give a figure of 

 the primary form of the substances described. 



Morphia, 



These crystals are very minute, and have 

 only one cleavage that 1 can perceive, paral- 

 lel to the plane h. The primary form is a 

 right rhombic prism, only the lateral planes 

 of which appear on the crystals. For these I 

 am indebted to Mr. R. Howard, of Stratford. 



M onM' 127° 20' 



Mon/i 116 20 



Aonc 132 20 



c on c' 95 20 



Tartaric Acid, 



The crystals from which this form has 

 been determined, were also given to me 

 by Mr. R. Howard. I have not suc- 

 ceeded in cleaving them, but the primary 

 form is an oblique rhombic prism. Fig. 1 

 exhibits the crystal as usually modified, 

 with the planes symmetrically placed. 

 Fig. 2 exhibits the same modified form 

 with the planes irregularly disposed as 

 they appear in most of the crystals, the 

 corresponding planes in both being marked 

 with the same letters. This anords an- 

 other instance of irregularity, which ren- 

 ders it not easy immediately to perceive 

 the relations of the several planes to each 

 other. 



Fig. I. 



