DESIDERATA, ETC. 
XXV 
MINERALOGY. 
Resolutions of the Committee. 
1. That Prof. Miller be requested to determine the form and 
optical characters of those Crystallized Bodies which have not 
been previously examined, and that chemists he invited to send 
him specimens of perfect artificial crystals. 
2. That Dr. Turner, Prof. Miller, Mr. Brooke, and the Rev. 
W. Whewell, be requested to cooperate in prosecuting and pro¬ 
moting the following inquiries, with a view to examine the the¬ 
ory of Isomorphism, and the connexion between the crystalline 
forms and chemical constitution of Minerals :— 
I. To determine whether the angles of varieties of the 
same species (in the usual acceptation of identity of 
species) are identically the same, under various cir¬ 
cumstances of colour, appearance, and locality; and if 
not, what are the differences ? 
II. To determine the chemical constitution of such va¬ 
rieties,—the specimens, mineralogically and chemically 
examined, being in all cases the same. 
III. To determine what quantity of extraneous sub¬ 
stances may be mixed with a crystalline salt, without 
altering its form. 
IV. To determine the angles of the various species or 
varieties of isomorphous or plesiomorphous groups,— 
and their respective chemical composition. 
Desiderata noticed in Mr. WhewelVs Report . 
1. To determine the optical differences on which depend the 
distinctions of the different kinds of lustre, metallic , adaman¬ 
tine , vitreous , resinous , pearly. 
2. To determine whether the oblique rhombic prism consti¬ 
tutes a real system of crystalline forms, or is a hemihedral form 
of the right prism. 
3. To determine the limits of magnitude and simplicity in 
crystallometrical ratios. 
4. To determine whether chemical groups are strictly iso¬ 
morphous or only plesiomorphous. 
5. To determine whether the angles of plesiomorphous cry¬ 
stals are separated by definite or by indefinite steps. 
6. To determine what are the differences of chemical compo¬ 
sition corresponding to differences of optical structure in re¬ 
sembling minerals, as apophyliite, tesselite, leucocyclite. 
