l63 



THE MICROSCOPE. 



cover them, and to prevent the excess from running out beneath the 

 cover upon the slide; whilst other subjects are so delicate that the 

 mere weight of the thinnest covering glass, pressing upon, would 

 crush them out of all shape. We will, therefore, with the reader's 

 permission, give some hints as to various methods of doing this be- 

 fore proceeding with other branches of our subject. 



Undoubtedly the most perfect cell, that has yet been devised, 

 is one of glass. For very shallow cells, to be used in mounting 

 diatoms, nothing can equal those cut from thin covering glass, such 

 as are used exclusively by Moller, in mounting his Typen- and 

 Probe-Platten ; and slides of arranged diatoms. These are cement- 

 ed to the slides by a thin layer of balsam, heated to such a point, as 

 to expel all, or nearly all of the turpentine; and nothing can excel the 

 neatness and perfection of their appearance and finish, whilst they 

 are, of course, quite permanent. 



Where deeper cells are required, those cut from glass tubes of 

 various diameters and shapes, or drilled from slips of different thick- 



nesses, and cemented to the slides with Marine Glue, are to be 

 highly recommended, as they are extremely neat in appearance, and 

 entirely permanent in character. The objections to all glass cells, 

 are the difficulty of preparing them by ordinary workers, and their 

 extreme costliness, if purchased ready made. If the latter consider- 

 ation, however, be of no moment to the reader, I would say by all 



