OF THE MICROSCOPE. 215 



the clutches, thus allowing the long sides to lie parallel to each 

 other, and at equal distances from the centre. A slide may 

 thus be grasped between them, and pushed along longitudin- 

 ally, as may be desired. 



Those who once see a turn-table, will find no difficulty either 

 in understanding the method of using it, or in putting this 

 knowledge into practice. The slide, being held on the table 

 either by springs or clutches, is made to revolve rapidly, and a 

 brush, charged with cement or varnish, is held against its sur- 

 face so as to leave a ring. There is a slight knack about making 

 good cells, which it requires a little practice to acquire. The 

 brush must be held in the direction of a tangent to the ring 

 that is, it must not point to the centre of the circle, but must 

 lie so that the ring, as it revolves, will draw the cement away 

 from the brush. Practice alone can give expeortness in doing 

 this, and we would advise the beginner to work steadily for a 

 few hours at making cells on pieces of common window glass, 

 strips of which can be had for nothing from any glazier. The 

 chief points to be attended to are the position of the brush and 

 the consistence of the cement. If the latter be too fluid, it 

 spreads and does not form a well-defined circle. If too thick 

 it does not leave the brush as freely as is necessary. The 

 method of preparing the cement will be explained under the 

 proper heai 



Fig. 68. 



Where a turn-table is not at hand, very good cells may be 

 made as follows: On a card draw the outlines of a slide with a 

 series of circles in the centre, as shown in Fig. 68; lay the 

 slide on the card so that the centre of the circles will be at the 

 centre of the slide, and then paint a circle of cement on the 



