. 
ON DIMORPHOUS BODIES. 209 
ture and more advanced state of the science, when observation 
shall have verified some, perhaps falsified the whole of our most 
likely predictions. 
XI. 
64. Relation of the Crystalline doctrine of Dimorphism to 
the Chemical doctrine of Isomorphism.—The differences hither- 
to observed between the properties of the two forms A and B of 
any dimorphous body are physical only ; if we impart to them 
unlike chemical relations also, they become tsomeric. 
65. The fact that two or more substances may consist of the 
same elements united in the same proportion, and have the same 
atomic weight, and yet possess unlike properties, chemical as well 
as physical, is at least as new to chemistry as the doctrine of 
dimorphism is to crystallography. Both classes of phenomena 
are due to a mechanical change in the relative position, distances, 
&c. of the particles of bodies ;—for what we call chemical differ- 
ences are only physical differences of a higher order. Those of 
isomerism, however, are more general, implying or carrying 
along with them those of dimorphism. Isomeric bodies in their 
several states not only exhibit different chemical properties, but 
assume also unlike crystalline forms, though the relations among 
these forms have not as yet been examined with that care which 
the subject deserves, and would probably well repay. 
66. Without affecting to understand how these two orders 
of differences are actually produced in nature, we can yet con- 
ceive how they might be produced under certain given conditions. 
For let the crystalline particles of which sensible crystals are 
immediately built up be prismatic—have three unlike axes— 
then according to the views of Voltz dimorphism may be ac- 
counted for. But let these crystalline particles be themselves 
groups (and we are certain that such a particle of a compound 
body must contain more than one, some many molecules), the 
Several members of which may be collocated at different distances 
or in different relative positions, and we have, independent of and 
beyond the supposed cause of dimorphism, another means of 
producing changes of a profounder character, which may affect 
the chemical relations of the crystalline particles while it alters 
also the relative lengths of their several axes. It is immaterial 
whether the ultimate molecules have the form of prisms, of ob- 
late ellipsoids, or of spheres; it is necessary only that by their 
collocation they may produce prismatic crystalline forms, and all 
the known phenomena can be conceived: According to this 
view, there is a strong analogy between the two classes of phe- 
nomena as regards the mode by which they are produced—the 
VOL. vi. 1837. P 
