2?8 PRACTICAL MICROSCOPY. 



moved, by means of a right-handed and left-handed screw, 

 a pair of clips which gripped the opposite and extreme 

 corners of the slip, as shown in Fig. 230. 



It will thus be seen that so long as the edges of the slip 

 are at right angles to each other the centering must be 

 absolutely accurate, but not otherwise. 



FIG. 230. 



On the introduction of this machine several operators 

 objected to the method of holding the slip, and Kinne soon 

 afterwards introduced his modification (Fig. 231), in which 

 the two corner clips were drawn together and made to grip 

 the glass slip by means of an indiarubber band or spiral 

 spring. 



In 1876 a notice appeared that Mr. Charles Butterworth, 

 of Shaw, near Oldham, exhibited at the annual soiree of 

 the Oldham Microscopical Society a turntable capable of 

 making cells of either circular or elliptical form ; and also 

 by its aid a thin cover-glass could be held in position on a 

 cell, whilst the various rings of cement or varnish could be 

 put on. It is constructed upon the principle of the " oval 

 chuck," and so enables either circles or ovals to be traced 

 with ease moreover, it may also be used for cutting thin 

 glass covers, either oval or circular, as well as for general 

 mounting purposes. 



