THE MICROSCOPE AND ITS PARTS. 31 



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 dissolves 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 ma- 

 chine called a " turn-table," manufactured for the pur- 

 pose. These turn-tables are as nice and neat and beau- 

 tiful 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 centre of the slip, and 

 the result is very pretty and very desirable if the be- 

 ginner can afford one, but he can get along right well 

 without. If you have none, draw in the centre 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 paste- 

 board. Of course the hand cannot be as steady as a 

 flat disk rapidly rotating on a central pivot, and the cir- 

 cles will not be as perfect, but they will be practically 

 as useful. To get the inked circle in the centre of the 

 paper, draw a lead-pencil line diagonally across it from 

 each upper corner to the opposite lower one, and use the 

 point at which the two lines cross each other as the cen- 

 tre of the circle. The glass slip can be kept in better 

 position, and the whole can be turned about, if the paste- 



