On Crystallography. 97 



must have leisure to seek each other, to apply to each other 

 by proper siirtaces, and to concLir all at the same tiuie to the 

 harmony vyhich ought to result troni their aggregation. The 

 liquid must be in a stale of repose ; its own molecuLs must 

 slowly abandon those of the mineral, in ordir to place tiicm 

 in the position most favourable to atiinitv, and the cavit> must 

 be spacious enough, and the liquid sufficiently abundant, for 

 the crystaHine moltcules to swnn in it at full liberty. 



If these conditions are not fulfilled, if it happens, for 

 instance, that the liquid is rapidlv evaporated, or that any 

 agitation is produced m it, these accidents, which we may 

 xeu-ard as disturbing causes of crystallization, will in some 

 measure disarrange the molecules, and force them to be tu- 

 multuously precipitated upon each other; and, as a neces- 

 sary consequence, the traces of the geometrical form which 

 would have taken place in the event of a slow and tranquil 

 aafsrc (ration will he more or less altered *. 

 "But^as we are only to speak here of crystallization properly 

 so called, an important consideration in the lirst place pre- 

 sents itself, — a consideration which places minerals by the 

 side of organic beings. In the vcgttable kingdom, for in- 

 stance, all the indivTduals of the same species seem to have 

 been made after one common model, /. e. their flower is 

 composed of parts equal in number and similar in figure 5 

 their leaves have the saaie arrangement, the same contours, 

 &c.— the diversities consist of but light and fugitive shades. 

 In short, when we have seen a single plant, we have seen the 

 whole species. 



It is totally different with respect to minerals. Frequently 

 crystals originating from one and the same substance assume 

 very difFerent forms, all equally distinct, and executed with 



* The crystals for;-ned in one and the same liquid around different centres 

 of action more or less closely connected with u'iich other, compose groups in 

 Nviiiv-h they are situated sometimes parallel to each ether, and somciimes 

 croisingeaih other in diflerent directions, in such a wny that they frequently 

 cnouijii appear to penetrate eacli other mutually. It also happens very gene- 

 rally that they are only salient ai; one of their parts, above the substance 

 which ^ervt-s'a5 a support to them. It is a fortunate circtimstance when a 

 crystal belonj's to the group only by a point, so that its position isolates it in 

 tome measure! and peruiits its form to be emiroly developed to the eyes of aa 

 observer. But most of the crystals which offer this advantage have been ex- 

 tracted from certain earthy masses in which they were really solitary, and in 

 the midst of which they are formed at the time when these earths weredilit?fi 

 in an aqueous (luid, We may conceive this formation Irom aa experiment of 

 Pelletier, who, having placed argil soaked in a soluiion of alum, cut ihts 

 ari'il into pieces when it v^as dry, and found laiernally crystals of alum of the 

 •ize of a pea Hence lie concluded that the crysialline molecules might have 

 bad if.e power of displachig thearaillace.uj mjlecu!e6,and ot rc:novmg thoje 

 obstacles whicli op'.-oced their union.— ^ifw. cl OL.seii}- rif Chtmi<i, t. ». p. »1. 



\o\.34. No. 130. Jiigust ie09. G similar 



