1899O Anderson. — Natural History Museum, Galway. 127 



the place of its youthful surroundings had brought back its 

 colour and true features. Several good photographs of 

 interesting bits of scenes are placed on the walls. The 

 Mineralogical Department is illustrated by crystal models 

 of the usual kind, glass and wood. A compromise is attempted 

 in giving effect to the views of the practical mineralogist, 

 like Professor Panebianco of Padua, who says that some 

 mathematical discussions concerning crystals tend to become 

 either childish or pedantic, and the views of the mathematician 

 who emphasizes the importance of the study of form, figure, 

 and molecular attraction. The type forms of Dana accord 

 with the practical instincts of the man who is constantly 

 handling minerals. Apparatus have been designed and placed 

 in this Museum, to illustrate the forces that are at work in 

 modelling crystals. Four cords above and four below mark 

 the edges of an octohedron in a simple way. The shape of 

 the octohedron is altered by the adjustment of weights and 

 the movements of sliding pulleys. The right octohedron of 

 the cubic system can be changed into that of the dimetric 

 and so on. The mind is thus led to dwell upon the effects of 

 the aggregation of forces. All the forces that make a body 

 spherical, would, if collected at the extremities of three 

 diameters standing at right angles, in such a way as to be 

 quite equal, thus be at work tending to develop an octohedron 

 in a cohering mass. The forces producing an ellipsoid might, 

 if reduced similarly to six, produce other right octohedra. 

 The Museum diagrams suggest a method by which form, 

 colour, and composition may be learned, at once, by the 

 student. Take a figure of carbonate of iron. The acid 

 constituent may be marked on one side, and the base on 

 another face. Anyone can colour the crystal, and, if a note 

 be added with reference to hardness and specific gravity, what 

 more does one want except a practical acquaintance with the 

 mineral itself, which can only be obtained by inspection, 

 testing, and handling? So one might put silica on one side, 

 and manganese on another side of rhodonite, figured, and 

 paint it flesh colour. By drawing such crystals an interesting 

 fact becomes impressed on the mind, viz., that impurities in 

 minerals are often associated with complications in the faces, 



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