THE MICROSCOPE. 163 



means use them, and nothing else, as they never give any trouble, 

 and are always neat and handsome in appearance. 



Block-tin makes a very good cell, which may be attached to 

 the slide by Marine Glue the same as glass, and which will contain 

 ftuid balsam quite as well ; but they must either be purchased of the 

 dealers, or made with a special and expensive punch. They are 

 more difificult to finish neatly than thost of glass, and are only re- 

 commended by reason of their comparative cheapness. Brass 

 curtain rings tnay be substituted for them, and if carefully handled 

 in the mounting, may be found permanent and satisfactory ; but my 

 own experience has not been favorable toward the latter, either as 

 to convenience of handling, permanency, or neatness of appearance. 



Fortunately we have a material, admirably adapted to making 

 cells, which any one can readily do for himself and at a trifling cost. 

 It is the ordinary white sheet wax used in artificial flowers and 

 which can be procured in three thicknesses, known 

 as "ordinary," "double thick," and" pond lily." A punch 

 specially constructed for cutting cells from these 

 sheets, can be purchased from the opticians at the 

 small cost of a dollar and a half ; and enough to 

 mount a dozen or more slides may be punched in a 

 few moments. 



WAX CELL PUNCH. 



A turn table is necessary for attaching these cells to the 

 slides, and some form of a self-centering one is recommended; the 

 enhanced first cost, being the only reason for hesitancy in making a 

 choice. A simple form of centering — not x^fZ/'-centering, mind you — 

 devised by myself many years since, in my early microscopical days, 

 and which costs but a fraction more than the simplest turn table 

 without it, has been found so satisfactory in my own work, as well 

 as that of many friends who have adopted it, that I am led to 

 describe it here and to give an illustration as well. Indeed, the 

 latter shows the simple device so well that further description is al- 

 most useless. A sheet of thin brass with a stop at the left hand end, 

 precisely one and a half inches from the centre, is attached to the 

 surface of the whirling table by a small milled head; by which the 

 distance of the edge of the brass plate from the table's centre may 

 be varied more than half an inch. A slide precisely 3x1 inches, 

 having been accurately centred on the table by means of the con- 



