Genth and Pen field — Contributions to Mineralogy. 381 



In figure 11 the filings in the regions near the poles are 

 drawn to the poles, leaving those regions bare. 



Fig. 12. Electro-Magnet — Iron Clappings. 



The somewhat fantastic field shown in figure 12 was ob- 

 tained from the same electro-magnet by employing coarse iron 

 chippings, instead of the finer iron filings used in the remain- 

 ing figures. The position of the bits of iron parallel to the 

 lines of force is distinctly shown. 



Note. — Since preparing the above, my attention has been called to the excellent 

 article of Professor Houston in the Electrical Engineer for July 20th, in which a 

 method exactly similar to the one here described was briefly outlined. This 

 furnishes snother instance of the simultaneous invention of a process by two 

 investigators, each working wholly without knowledge of what the other is doing. 



Art. XLYI. — Contributions to Mineralogy, No. 54- / by 

 F. A. Genth. With Crystallographie Notes; by S. L. 

 Penfield. 



1. Aguilarite. 



Since the publication of my investigations on aguilarite,* 

 I had an opportunity to examine quite a number of specimens 

 of this mineral. Only a very few small fragments of pure 

 aguilarite in skeleton dodecahedrons, like the original, were 

 found among them ; most of them were altered, as previously 



* This Journal, xli, 401. 



