282 PRACTICAL MICROSCOPY. 



been introduced by Mr. H. P. Aylward, of Manchester, 

 and may be said the simplest, least expensive, and best 

 self-centering turntable extant. 



FIG. 235. 



The author, from actual experience, can recommend it 

 as being the turntable for all the wants of the microscopist. 

 Mr. Aylward calls it the " Concentric." It essentially 

 consists of two plates, the inner revolving on a pivot, 

 whilst the outer revolves concentrically on the inner, .a few 

 small pins being so arranged that by a single turn of the 

 outer ring they firmly grasp the glass slide, and cause its 

 centre to exactly coincide with the centre of the turntable, 

 whilst a simple reverse movement instantly liberates it. 

 This turntable answers for slides of various widths, from 

 I inch to 2j inches, it is strongly made, and well finished, 

 besides which loose springs are supplied, fitting into corre- 

 sponding holes in the turntable, convenient for making 

 rings in any other position than that of the true centre of 

 the slide. 



This instrument is shown in Fig. 236, the letters being 

 explained as follows : 



A, ordinary wood block with steel pivot, on which the 

 brass table revolves. B, two brass springs which fit into 

 holes in the table, and may be used when the slide is 

 required to be out of centre ; when not in use they fit 

 into holes in the wood, as shown above. D, revolving 



