782 Museum of Economic Geology [No. 118. 



facilities of intercourse, as may be expected to awaken to new life the 

 commercial energies and enterprise of the valuable districts, through 

 which it will pass, 



4. Since it may be expected that many of those persons willing to 

 Requisites for the avail themselves of the existence of the Museum to 

 e^lrrSlrlTralt*: become acquainted with the principles of Economic 

 of Minerals. Geology would require information of the most 



elementary character, I consider it would add to the useful effect 

 of the Museum, were measures adopted to facilitate the acquisition of 

 such knowledge. As addressing themselves more immediately to our 

 senses, the external characters of minerals first claim attention, and 

 among these, the high importance of crystalline form, arising from its 

 constancy in the same substances, naturally suggests that some mea- 

 sures should be taken for the illustration both of the general principles 

 of Crystallography, and of the manual operations by which these are 

 practically applied to the determination of particular bodies. For the 

 former object, it would I think be found most useful to have a series 

 of model crystalline forms, so arranged, as to exhibit distinctly, those 

 varied, yet determinate modifications of certain primary forms, which 

 are found to exist among crystallised bodies in nature ; for the latter 

 purpose, goniometers, or instruments for the measurement of angles of 

 crystals, both of the common compass and reflective kinds, ought to be 

 provided. Those brilliant optical phenomena exhibited by minerals, 

 possessing the property of double refraction, under the influence of 

 polarized light, and which furnish us with new means of referring 

 these minerals to the systems of crystallisation of which they may be 

 members, require for their display an apparatus of the most simple 

 character, consisting only of a few pieces of common glass, and any 

 non-metallic reflecting surface. For the determination of the important 

 property of specific gravity, a hydrostatic balance, or properly con- 

 structed hydrometer would be essential, while, a small magnet and 

 electrometer would be necessary for ascertaining the magnetic or electric 

 properties of any mineral under examination. Separation of the most 

 important characters is elicited by the employment of the blow-pipe 

 in the examination of minerals. This therefore, with its necessary 

 accompaniments of fluxes, &c. would be required, and with the 

 addition of a few minor articles, as files, knives, pincers, &c. would 



