Mr Haidinger on Regular Composition vn Crystals. 59 



margin of the lower one, and about the centre towards which 

 the polarized bars of the cirrostrati seemed to converge, a dark 

 space of considerable magnitude, from which rays began sud- 

 denly to shoot out, of the same dark appearance, towards the 

 upper cloud ; these rays, however, did not continue their dark 

 aspect, on reaching the upper cloud, but seemed rapidly to 

 dissolve that cloud in stripes, so that very quickly the upper 

 cirrostratus was completely torn into shreds by these rays, 

 and when they had passed, the stars could be seen through 

 the cloud. By and bye, the cloud began to form precisely 

 in the same manner as it had dissolved, and no more rays 

 came from the lower one: the two clouds finally inosculated, 

 and covered the sky with a general haze. Can this phenome- 

 non be considered analogous to the one already described as 

 having occurred on the 11th of February ? 



Nothing else of any consequence, except a fine Solar Coro- 

 na on the 13th December, was seen before the close of the 

 year. 



Leith, February 1825. 



Art. IK. — On the Regular Composition qf Crystallized Bo- 

 dies. By William Haidinger, Esq. F. R. S. E. Com- 

 municated by the Author. — {Continued from Vol. III. p. 

 93.) 



III. Pyramidal System. 



The situationof the plane, in which two individuals, whoseform 

 belongs to the pyramidal system, may be joined in aregular com- 

 position, and the situation of the axes of the individuals them- 

 selves, as in the rhombohedral system, produce a general dis- 

 tribution of these compound bodies into two classes. Either the 

 axes of the two individuals are parallel, or they include an 

 angle. In the latter case, the face of composition is always 

 parallel to a face, or perpendicular to an edge of an isosceles 

 four-sided pyramid, and this kind of composition may take 

 place in any class of forms of a pyramidal species. But, 

 if the axes of the individuals are parallel, and the situation of 



