J. D. Dana on Cohesive Attraction. 



367 



mental axial lines or axes of attraction. Thus the molecule of a 

 cube must have equal axes, like the cube itself; that of a prism, 

 like axes with the prism in relative dimensions ; and if oblique, 

 the axes should have the same degree of obliquity. This state- 

 ment with regard to molecules is potentially true ; and in this 

 sense, the only one in which we now speak of molecules at all, 

 it is no hypothesis. 



The actual forms of molecules constitute another considera- 

 tion, and one for which we have less precise data. The molecule 

 of a cube may be either a sphere or a cube, as either form would 

 produce a cube by the same mode of aggregation ; and that of a 

 prism may be either a similar prism or a spheroid of like di- 

 mensions. This is illustrated in the annexed figures 1, 2, 3. 



Fig. l. 





Fi 



g.2. 







r~ l!'' 







yy 



Fig. 3. 



We cannot therefore determine absolutely the form of the mole- 

 cule from the form of the crystal. But from the greater simplicity 



of the hypothesis that molecules are spheres and spheroids, its suf- 

 ficiency to meet every case in nature, its necessity to explain opti- 

 cal phenomena, and other considerations we have presented else- 

 where, we adopt in this place the view of their spheroidal 

 forms. 



By having some idea of a molecule in the mind, we may 

 toore easily conceive of the principles deduced 



with regard to 



to the molecule 



the three 



cohesive or molecular attraction. 



Our first inference, expressed with reference 

 ^ r iU therefore be the following : 



1 Molecules in solids have fixed relative dimensions for each 

 fond of matter, and certain axial lines of cohesive attraction 

 w hich are fixed in direction :— and we add, as a necessary truth, 

 whose force is inversely related to their length. 



Viewing the molecules as spheres and spheroids, 

 a *es are the three conjugate axes or conjugate diameters of these 

 forms.* The attraction is not supposed to be confined to the 



" If the conclusion be correct that the molecule of the element gold is a simple 

 sphere because of its cubical crystals; and that of sulphur an cih.psoid from the 

 u "oqtial axes of its crystals ;— it is as good also with rf-nrd to compounds Hence 

 lh e molecule of pyrin (a compound of sulphur and iron), whose crystal is a cube 

 *•« he a sphere ; and that of alum, a spheroid, fcc It matters not whether we 

 can conceive or not of two molecules of sulphur and one of iron, different in size 

 ai, d shape, uniiinor go as to make a simple sphere. The conclusion is one not de- 

 P^ulent for its truth on our conception The finite mind is an interjnHer oi na- 

 lui *e and may not presume to the rank of dh tator. Its conception! will be as in- 

 ane with rt'gard to any kind of combination or mode of aggregation in the above 

 c . as «, which could pro'duce out of such means a symmetrical cube with its facet 



Umilar in lustre and e\ery other physical character. 



