SECTION II. 

 MOLECULES. 



The homogeneous molecules which are aggregated 

 together in the production of crystals, are supposed 

 to be minute, symmetrical, solid particles, contained 

 within plane surfaces. They are also conceived to be 

 again separable from each other by mechanical divi- 

 sion, which however stops very short of the separa- 

 tion of single molecules from the mass which has been 

 formed by their union. 



For, however minutely we may divide a piece of 

 carbonate of lime, we cannot imagine that we have 

 ever obtained any single portion or molecule contain- 

 ing only one atom or proportion of carbonic acid, and 

 one atom or proportion of lime. 



This effect of mechanical division merely implies 

 that the molecules are separated at their surfaces by 

 cleavage, and are not divided or broken. And it thus 

 serves to distinguish them from the elementary par- 

 ticles or atoms which enter into their composition, 

 and which cannot be separated from each other but 

 by chemical agency.* 



* Although it is not immediately connected with Crystallography, 

 I am induced to state an observation here which has occurred to me 

 relative to the forms of the homogeneous molecules of minerals, when com- 

 pared with the forms of the atoms , or elementary particles, of which those 

 molecules are composed. 



We certainly know nothing of the forms of the atoms of those elemen- 

 tary substances which do not occur crystallized, such as oxygen, hydro- 

 gen, and many others. But we infer from analogy that the atoms of 

 sulphur, carbon, the metals, and such other elementary substances as 



