186 SEVENTH REPORT—1837. 
every group of isomorphous bodies presents us with additional 
illustrations. Not only may we expect that entire groups shall 
prove to be dimorphous, of which we as yet Anow only one or 
two really to be so, as the carbonates of which those of lime 
and lead, and the sulphates of which that of nickel is the type ; 
but groups also not even recognised as yet to be isomorphous, 
though their chemical formule are analogous. Thus the tung- 
state of lime and that of lead occur in square prisms, that of iron 
and manganese (wolfram) in oblique rhombic prisms, but since 
all these compounds are represented by the same formula R Tu, 
the form which one assumes should not be impossible to the 
other. We know that lime and protoxide of lead are dimor- 
phous in their carbonates ; we may expect them to be so also 
in their tungstates, and since lime and the first oxides of iron 
and manganese are capable of mutually replacing each other, 
wolfram may be looked for in square prisms. It has indeed 
been frequently observed by mineralogists of this form. At 
Huel Maudlin, in Cornwall, at Schénfeld, and elsewhere in 
Saxony* it has occurred in square prisms, but these are univer- 
sally stated to be pseudomorphous, to be casts of previous cry- 
stals of tungstate of lime. I have never had an opportunity of 
examining any of these crystals, but as bearing on the very in- 
teresting question how far second forms at least may be inferred 
from chemical formule, the supposed pseudomorphism of the 
square prisms of wolfram is deserving of a close examination.{ 
But if dimorphous substances may be so numerous, why are 
they not so in ordinary circumstances, or why have they not 
been more frequently observed? Ten years more can scarcely 
pass without adding greatly to the number of known cases of 
dimorphism, and suggesting some probable reply to this and 
other similar questions. If the chemical affinities which two 
bodies are capable of displaying towards each other may lie 
dormant, even when the bodies are in juxta-position, till the 
proper hygrometric or thermometric conditions be attained, so 
may it be with the molecular attractions by which particles are 
* Allan’s Manual of Mineralogy, p. 219. 
+ Since the above was written I have seen Cornish specimens of this mineral 
in the collection of Mr. Brooke. They are in octohedrons, some of them beauti- 
fully perfect; the greater part of them, however, more or less hollow, and cer- 
tainly presenting the appearance of after crystals. Still we are not to despair of 
finding crystals of wolfram belonging to the pyramidal system, and our search 
may perhaps be stimulated by the character of its twin crystals, which seem 
to indicate that though this mineral presents itself in the form of oblique prisms, 
it may in reality have rectangular axes.—See Arystallographie von Gustav Rose, 
p- 119, and Whewell’s Report on Mineralogy, p. 332. 
