114 The Microscope. 



In looking over the price lists and catalogues from the various- 

 dealers in microscoi^e accessories, I find the following formidable- 

 list of turn tables are on the market ; Shadboldt's with •wood 

 base, same with centring adjustment ; Cox's improved self centr- 

 ing ; Standard ; National, plain and self centring ; Griffith's self 

 centring and decentring combined ; Queen's comfortable turn 

 table ; Kinne's self centring ; Congress self centring ; Beck's ;. 

 Watson's plain and self centring ; National, volute, and probably 

 several others which I have not seen. 



According to the price, turn tables are divided into two great 

 classes : self centring and plain. By self centring is meant that 

 a slide which has been ringed on the turn table can be again 

 placed in exactly the same position without trouble. This is a 

 convenience when more than one coat of the cement must be 

 applied to a cell. In the mounting of opaque objects and all 

 substances requiring deep cells, the self centring arrangements 

 will be highly appreciated. I have found that the slides in the 

 market of average quality are not perfect rectangles, so that the 

 slide must be replaced end for end the same as before, in order 

 to have the entire benefit of the self centring apparatus. This 

 can be accomplished by marking one side of the turn table disk 

 with a file or by spotting it with cement. Then place the end 

 of the slide bearing the label, or some special mark, towards the 

 mark on the disk. An observence of this simple rule will save 

 much annoyance in retouching or finishing off mounts. I wouldi 

 suggest that manufacturers make the disks with a mark where 

 one end of the slide is placed. 



The decentring turn tables are so arranged that a slide finished 

 off on a plain table can be readily brought into position and 

 retouched. I have found this device of great convenience when 

 fixing up old mounts or those injured in transportation. The 

 Griffith turn table has the best decentring arrangement that I 

 have ever used. 



Do not hesitate, in selecting a turn table, to purchase a self 

 ceiitring and decentring one, if it can be afforded. At any rate 

 get one that has a heavy disk and a substantial hand rest so that 

 the instrument will set firmly on the work table and the disk 

 will continue to revolve for some time. A smooth ring of cement 

 cannot be made if the brush touches the slide while the disk is 

 at a stand still, or moving slowly. The light turn tables with thin 



