1881.] NATURAL SCIENCES OF PHILADELPHIA. 501' 



In the department of instruction much is needed. Before any- 

 systematic instruction in crystallography can be given, the 

 Academ}^ should have a set of the Siegen glase crystal models for 

 instruction, and a collection of wooden models for practice. For 

 advanced mineralogical instruction it is also necessary to have 

 certain instruments, among which a reflecting goniometer, a 

 polariscope, and a lithological microscope are the most important. 

 A good balance is also desirable tor accurate specific gravity deter- 

 minations. These instruments would be used both for instruction 

 to advanced students, and, under proper restrictions, for original 

 investigations. 



Henry Carvill Lewis, 



Pj'ofessor of Mineralogy. 



