MICROSCOPIC OBJECTS. 147 



a flat board, and rub the edges until quite smooth. If a 

 bright edge is preferred, it may now be instantly passed 

 through the flame of the spirit-lamp. 



Slides made in the manner above described are very 

 durable, and the preparation will not be liable to injury 

 from damp. We have now under inspection a collection 

 of several hundred slides of recent woods, British mosses, 

 crystals for polarization, &c. &c. mounted in this way, 

 which after the lapse of fifteen years are as perfect as on 

 the day they were put up . 



(7.) Second Method of Preparing Glass Slides for 

 Sealing. — ^This plan has some advantages over the first, 

 as it enables you to employ very thin plates for covering 

 the object ; but it is more liable to injury. The lower 

 plate should be of thin plate glass about -jq^^ ^^ ^^ ^^^ 

 thick, the edges carefully squared ; the upper plate may 

 be as thin as required ; it must be cut about ^^th of an 

 inch shorter and narrower than the lower one. After the 

 object has been arranged upon the lower plate, the upper 

 one is to be placed over it in such a manner as to leave a 

 uniform margin around the lower plate. By this means 

 a rectangular groove is formed, which is to be filled with 

 sealing-wax. As the upper plate is usually thin, the best 

 and strongest cement for this purpose is japanner's gold 

 size thickened with a little vermilion, or when that colour 



is not desirable, lamp-black. Note. — When the objects 



are mounted in a fluid or spirits, vermilion is objection- 

 able, the mercury being liable to chemical change. 



(8.) Mounting Crystals for Polarizing Microscope. — ■ 



