RECOMMENDATIONS. 477 



1 ,) 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 circumstances of colour, 

 appearance, and locality ; and if not, what are the differences. 



2.) To determine the chemical constitution of such varieties, 

 — the specimens, mineralogically and chemically examined, 

 being in all cases the same. 



3.) To determine what quantity of extraneous substances 

 may be mixed with a crystalline salt, without altering its form. 



4.) To determine the angles of the various species or vari- 

 eties 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, ada- 

 mantine, 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 

 crystals are separated by definite or by indefinite steps. 



6. To determine what are the differences of chemical com- 

 position corresponding to differences of optical structure in re- 

 sembling minerals, as apophyllite, tesselite, leucocyclite. 



GEOLOGY. 



*1. That measurements should be made, and the necessary 

 data procured to determine the question of the permanence or 

 change of the relative level of Sea and Land on the coasts of 

 Great Britain and Ireland ; and that for this purpose a sum not 

 exceeding £100 be placed at the disposal of a Sub-Committee, 

 consisting of Mr. Greenough, Mr. Lubbock, Mr. G. Rennie, 

 Professor Sedgwick, Mr. Stevenson, and the Rev. W. Whewell : 

 — the measurements to be so executed as to furnish the means 

 of reference in future times, not only as to the relative levels 



^ Professor Miller reported the progress of these inquiries to the Cambridge 

 Meeting. 



