438 On Crystallography , 



the principal character of the sciences. I have known 

 some admirers of simjile and imaided ocular demonstra- 

 tion, nevertheless, approve of using an eye-glass. Now 

 what is a goniometer but a kind of {geometrical eye-glass, 

 which enables us to percci^^e those minute diflerenccs, and 

 imperceptible gradations, which escape the eye? 



With respect to ])lanc angles, we have sometimes indi- 

 cated them also*, particularly those of primitive forms, 

 and those which imprint on secondary forms a character 

 of simplicity and regulariiVj such as the angles of 90°, 

 60\ 8cc. 



We shall conclude from what precedes, that every cry- 

 stalline form, when we consider only what is invariable in 

 \t,i.e. the number and the respective inclinations of its 

 faces, is so truly characteristic, that it may serve of itself 

 to determine, independently of every other consideration, 

 the species to v/hich the crystal belongs that presents it, 

 provided it be not a cube, a regular octahedron, a regular 

 tetrahedron, a rhomboidal dodecahedron, or a regular hexa- 

 hedral prism. Thus the form '^f the dodecahedron with 

 triangular scalene faces inclined arriong each other alier- 

 iiately by li4" 2(/ 20'', and 101" 28' '40", indicates by 

 itself a variety of carbonated lime. 



Hence it would be possible to compose a method, by 

 means of which, any crystallirve form bejng given, we 

 might succeed in ascertaining in what species if ought to 

 be placed- 



It is easy to perceive, that by considering the faces of 

 crystals relative to their number which varies froin four to 

 60 and upwards, with ihcir vertical positions, inclined or 

 horizontal, with the other modes of existence of which 

 they are susceptible, we should have divisions and subdi- 

 visions so much the clearer, if geometrv was called in to 

 determine and circumscribe ihem. A method of this 

 kind would be purely factitious, but it would fulfil its 

 principal object : and we might even conceive that a geo- 

 iDctrician with its assistance, who was no naturalist, and 

 who had only before his eyes the collection of crystalline 

 forms executed in wood, might succeed in arranging this 

 eollection. There would only be the forms conmion to 

 various species which would lead to several names, amoiig 

 which we could only choose from the inspection of th« 

 natural crystals, by combining with the form a second 



• V\e may nensurc these anHes by means of a card properly cut, or by 

 tn^'o very thin rules of steel; whicji turn on each other by means of a hinge, 



character 



