4§6 PHYSICAL GEOGRAPHY. 



and gradually collect in the phial, which can then be removed and tightly 

 corked, and another substituted. Some very beautiful forms have been 

 procured in this way. The stain occasionally seen on the surface of the 

 sea in some latitudes, as well as the minute organisms causing the lumi- 

 nosity of the ocean, yield rich crops of diatoms, and should be secured. 

 Such gatherings may be put up as obtained, or have alcohol added to 

 them for better preservation. The collection of aquatic plants from the 

 mouths of rivers is extremely desirable, — such as have been made in the 

 delta of the Ganges yielding interesting results. The refuse of dredging 

 for shells often yields mud, old shells, or algae ; and collectors will do well 

 to secure such. Experience, however, will teach the best places to look 

 for recent diatoms ; but the above general directions will prove of service 

 to those who are new to the pursuit, or who collect for others. 



It should always be remembered that a knowledge of the exact locality 

 is of the greatest importance, — so that upon the label should be written 

 in ink the locality, date of collection, and name of collector. Other 

 facts deemed of interest may also be added. 



PART EIGHTH. 



How to Prepare Specimens oe Diatomace/E for Examination and 

 Study by Means of the Microscope. 



Having accumulated a number of gatherings of rough material, which, 

 a cursory examination has shown, contain specimens of diatomacecc, and 

 which, it is judged, it will answer to clean and otherwise arrange and put 

 up, or, as it is technically termed, "mount," for future study, the intend- 

 ing diatomist requires to be informed how he may best set about pre- 

 paring his specimens in the most advantageous manner. The author of 

 the present sketch has published, in the seventh volume of the Proceed- 

 ings of the Boston (Mass.) Society of Natural History, certain directions 

 for collecting, preparing, and mounting diatomacex for the microscope; 

 and, as that paper contains a large part of the information he desires to 

 impart at the present time, he will draw upon it pretty freely, supple- 

 menting it to such a degree as later investigations warrant, or as may 

 seem desirable. 



Although most of the published treatises on the use of the microscope 

 in general profess to give directions for mounting objects in such a 



