230 



SELECTION AND USE 



melted condition, by means of a brush, to the warm glass slide. 

 The object should not be stuck on with turpentine or similar 

 cement, but should be attached to the wax after a small spot 

 on the latter has been softened by bringing near it a hot wire. 

 Objects mounted in this way, in cells so prepared, seem to re- 

 main in good condition for years. 



A very ingenious cell has been devised by Mr. D. B. Scott. 

 This cell is punched out of thin sheet metal, as shown in plan 

 and section in figures 76 and 77. The cell is formed by the 



Fig. 76. 



Fig. 77. 



METAL SLIDE AND CELL FOR OPAQUE OBJECTS. 



central depression, and there is a turned-down edge all round 

 the slide which gives it strength, and causes it to lie steadily 

 on any flat surface. The cell has a ledge, or rebate, as seen in 

 figure 77, for the purpose of supporting the thin glass cover. 

 When made of tin the whole slide is japanned; those made of 

 brass are lacquered, and the interior of the cell is covered with 

 black asphalt, or some similar dark varnish. The objects are 

 attached to the surface of the varnish by means of gum water, 

 to which a very little glycerine has been added, and the thin 

 glass cover may be cemented down and varnished on the turn- 

 table in the usual manner. 



Fig. 78. CELL FOR OPAQUE OBJECTS. 



The alleged failure of the wax cell gave rise to a great many 

 devices, one of which, proposed by Mr. Atwood, consists of a 

 vulcanite or hard rubber cell, of which a sectional view is 

 given in figure 78, the dotted lines showing the thin glass 



