168 SEVENTH REPORT—1837. 
Il. 
15. Of Isodimorphous Groups.—In my report on the ac- 
tual state of chemical science, published in 1832, p. 433*, I 
drew attention to the remarkable fact that two substances 
known to be dimorphous, the carbonates of lime and lead, cry- 
stallized each in two forms, the analogous pairs of which were 
also isomorphous. ‘To distinguish this new character I sug- 
gested the term isodimorphous, and I stated as probable that 
we should *‘ soon be able to embrace the whole of the isomor- 
phous groups to which calc spar, and arragonite severally 
belong in one large isodimorphous group.” This expectation 
has already been partly verifiedt, while other groups have been 
discovered connecting other systems of crystallization also, and 
holding out the promise of large accessions to this branch of 
knowledge as observations become more extended. 
16. The following table comprises all the groups of these 
substances, and all the members belonging to these groups with 
which we are at present acquainted. 
* Report of the British Association, vol. i. 
+ See especially the interesting paper of G. Rose, (Pog. An. xlii. p. 366), 
whose experiments are still in progress and promise new accessions to this list, 
as well as to our knowledge of the circumstances under which the several forms 
are produced. 
