MICROSCOPIC OBJECTS. 143 



rule made as follows. Select a piece of well-seasoned 

 mahogany or other suitable wood having its surfaces 

 planed smooth and flat ; let it be about 15 inches long 

 by 10 inches wide. Along one side attach a raised edge, 

 to project about fths above the general level. Having 

 determined the length and width of the glass-shdes you 

 intend to adopt, procure a cutting- diamond, the best 

 form of mounting for which is the Patent Plough. This 

 done, provide yourself with two rules about 12 inches 

 long and |^th of an inch thick ; the one for cutting the 

 glass of the proper length, and the other for the breadth 

 of the slide. Ascertain the breadth of the steel mount- 

 ing of yom' cutting- diamond, which is usually ^(jth of 

 an inch, and let the width of each rule be half that 

 quantity less than the measure required. Thus for cut- 

 ting slides 3 inches long and 1 inch wide, the rules 

 should be 2 -Jfths long and ^§ths wide. To use this 

 board, having cut one side of your plate of glass straight, 

 place it on the board with its straight side close to the 

 raised edge, then take the broad rule which determines 

 the length of your shdes and place it upon the glass 

 likewise close to the raised edge. Draw the diamond 

 across the glass, holding the handle between the 

 two fore-fingers in an inclined position, and make the 

 cut. The amount of pressure upon the diamond, and 

 the inclination, are best determined by practice. Cutting- 

 diamonds require to be of different sizes according to the 

 thickness of the glass to be cut. The ordinary glazier's 

 diamiond is suited for window-glass, but for thick pk 



