0/1 Crysiallography, JD3 



tnay cause the other characters tO; vary* Thus, in order 

 that we may not quit the example of feldspar, such in this 

 substance is the arrangement of the natural joints, that the 

 molecule resulting from it is an oblique-angled parallelopi- 

 pedon, in which the three plane angles which concur to the 

 formation of one and the same solid angle, form among 

 them a first angle of 90°, a second of 120°, and a third 

 of inland a half; and these angles will be constantly 

 the same in specimens variously crystallized ; in those which 

 will give by analysis barytes or potash, as well as in those 

 which will exhibit no vestie^e of it. 



And not only may we estimate by observation combined 

 ■with theory the angles of the integrant molecule, but we 

 even succeed in ascertaining the relations between its di- 

 mensions, and there results a geometrical form perfectly 

 determinate, which is the same in all the individuals of 

 the species, and which presents as it were a fixed point in 

 the midst of the oscillations of all the other characters ; so 

 that we may even say, that in general the bodies of each 

 species touch closer in the rip-sults of the theory relative to 

 their structure than in those of chemical analysis. 



T do not pretend to raise the character I have just 

 mentioned above its real importance. I am even led to 

 suspect the predilection which 1 ought naturally to have 

 for that character which belongs to a branch of mineralogy 

 which I have cultivated with particular care. But this 

 predilection does not prevent me from stating a trutl^ 

 which T think useful to the progress of science ; which is> 

 that this character, borrowed from the structure, ought to 

 have a great influence in the distinction of the species; and 

 by neglecting it we deprive ourselves of one of the most 

 advantageous methods for the formation of an exact and re- 

 gular system. 



It may be objected, that the determination of the inte- 

 grant molecule of a body is frequently a delicate operation, 

 which requires minute experiments, and besides presup- 

 poses a knowledge of calculation which the whole world is 

 not in possession of. But chemical analysis has also its 

 difficulties, and is not the affair of a moment. It requires 

 a good deal of art to employ the most proper agents for 

 seizing and coercing principles invisible, and, if we may 

 l>e allowed the expression, impatient to escape from the 

 bands of the chemist: it requires art also that the operation 

 may take nothing from the result that bek>ngs to it, and 

 a<ld nothing that is foreign to it; and sometimes it is only 

 by repeatedly recurring to the subject, that we succeed 



Vol. 35. No. 143. March 1810. N in 



