THE MICROSCOPE AND ITS PARTS. 29 



can be easily prepared by the novice, is simply shellac 

 dissolved in alcohol. The solution can be made as 

 thick as is desired by allowing some of the alcohol to 

 evaporate, or it can be thinned by the addition of 

 more. It should be thick enough to flow freely from 

 a small camel's-hair brush, but not so thin as to spread 

 in an irregular film over the glass. As shellac dis- 

 solves slowly in alcohol, it is better to add more of the 

 latter than will be needed, and to thicken the solution 

 by evaporation. It will keep for any length of time in 

 a tightly closed bottle. 



A ring can be built up with a camel's-hair brush, and 

 this cement, either by the hand alone, or by a little 

 machine called a "turn-table," manufactured for the 

 purpose. These turn-tables are as nice and neat and 

 beautiful as can be imagined, and they cost — the 

 cheapest that I can find in the catalogues costs $2.50. 

 They spin perfect circles exactly in the center of the 

 slip, and the result is pretty and desirable if the be- 

 ginner can afford one, but he can get along right 

 well without. 



If you have none, draw in the center of a strip of 

 white pasteboard the size of a slip, a circle in black 

 ink, and use it as a guide to the brush with which you 

 make the ring after the slip is laid on the pasteboard. 

 Of course, the hand cannot be so steady as a flat disk 

 rapidly rotating on central pivot, and the circles will 

 not be so perfect, but they will be practically as useful. 

 To get the inked circle in the center of the paper, 

 draw a lead-pencil line diagonally across the parallel- 

 ogram, from each upper corner to the opposite lower 

 one, and use the point at which the two lines intersect 

 as the center of the circle. The glass slip can be kept 



