THE MICROSCOPE. 179 



profitably employ his instrument is in the minute structure of 

 molluscan shells, especially those of fossil Brachiopoda. Here, also, 

 Dr. Carpenter has been conspicuous; but no American observer has 

 given this field of investigation as much attention as the late Mr. F. 

 B. Meek, who succeeded in closing the evidence, by this means, as 

 to the distinctness of two genera long in dispute. The investiga- 

 tion of fossil structures by means of thin sections, is an inviting 

 field just opening for the entrance of patient and thorough students. 



Quite as recent is the microscopic method of lithographical study. 

 Lasaulx, Rosenbusch, Zirkel, and others in the old world, have shown 

 that thin sections of crystalline rocks reveal their mineral composition, 

 and present at the same time preparations of unique beauty, well 

 suited for the use of the polarizer. Professor Julien, of New York, 

 has engaged extensively in the productions of thin sections, using 

 a somewhat costly lathe of his own construction. Prof. Julien .ap- 

 plied this method to the rocks of Michigan; Mr. Hawes to those of 

 New Hampshire, and N. H. Winchell, to those of Minnesota. Dr. 

 Rominger, of Ann Arbor, however, produces equally five specimens 

 by hand, with no accessories but a copper plate and one quality of 

 emery. He devotes about an hour to the completion of a specimen. 

 An enterprising and patient worker may, therefore, obtain all the re- 

 quisite sections of rocks and fossils, whether calcareous or silicious, 

 without any costly or complicated appliances. 



Should this subject seem to possess sufficient interest, the ap- 

 pliances, manipulations and principal published helps may be 

 brought into notice on some future occasion. 



SOME HINTS ON THE PREPARATION AND MOUNTING 

 OF MICROSCOPIC OBJECTS. 



BY W. H. WALMSLEY. 

 FOURTH PAPER. 



HAVING thus far in our practical work of preparing various 

 objects for examination under our microscopes and for per- 

 manently preserving the same, confined ourselves to balsam and 

 dry mounts, it seems proper for us to make a beginning, at least, in 

 fluid mountings, which, after all, are the most generally useful and 

 valuable. So many delicate and beautiful structures are com- 



