Formation of Compound or Twin Crystals. 275 



formed, challenging every possible or conceivable degree of appro- 

 bation, according to their varied merit ; as, on the contrary, bad ones 

 are performed, which must receive every possible variety of disap- 

 probration, according to the infinitely varied degree of demerit which 

 they possess. The names of intellectual objects, such as attention, 

 memory, imagination, &;c. stand upon the same footing, and are 

 open to the same observations with those of moral impressions and 

 moral determinations. 



"Besides the knowledge of invisible objects, there a-re some branch- 

 es of it, which are founded upon the great instrument, viz. language, 

 which keeps up the communication between visible and invisible 

 objects, as far at least as that communication depends upon our ac- 

 quaintance with the thoughts of other men. The principal sciences, 

 the most noted sciences, that come under this description, are gram- 

 mar, rhetoric, and criticism. These may be considered as compre- 

 hending under them, all the rales, directions, and observations that 

 relate to the use, the improvement, and the embellishment of lan- 

 guage, regai-ded as a vehicle of thought. 



But as this paper has akeady been extended far beyond the lim- 

 its within which I at first expected it to be confined, I shall reserve 

 the observations I intended to make on these subjects, with some 

 others on moral definitions, which I have not completed, for the 

 ground work of some future speculations. 



Art. VI. — On the formation of Compound or Twin Crystals ; by 

 James D. Dana. 



Read before the Yale Natural History Society, March 3, 1836. 



The nature of atoms or those invisible particles which have been 

 supposed to constitute matter, has long received the attention of the 

 philosophic w^orld. Till within a few years, the theories on this 

 subject have been a collection of mere speculations. Like the met- 

 aphysics of the mind, thought, aided it may be by the sensations, 

 but unassisted by any inquiries into the nature of matter itself, has 

 been considered fully capable of furnishing both facts and princi- 

 ples ; as if attempts to deduce conclusions from the visible to the in- 

 visible, were as futile in material as in mental investigations. The 

 more philosophical methods of scientific inquiry of modera times, 



