Cross-line Oculars. The process of centring the object-stage or the ob- 

 jective by means of special centring appliances as well as in investigations in 

 polarised light requires that the centre of the field should be indicated by a mark 

 in the plane of the diaphragm of the ocular. For this purpose we supply glass 

 discs ruled with cross-lines for dropping into the ocular. 



The addition of such a disc raises the price of an ocular by Marks 4. . 

 If it be also desired to have the eye-lens adjustable, a further charge of Marks 7. 

 is to be added. 



In subsequent ordering of the glass disc ruled with cross-lines it should 

 be stated whether the discs are intended for ordinary oculars or oculars with 

 adjustable eye-lens. 



's Prism and Capillary Rotators. 



These two instruments are more especially designed to facilitate the examin- 

 ation, from different sides in succession, of objects so small that the control of their 

 movements under the microscope would be difficult to accomplish by hand. 



Nos. 196 and 107. Prism Rotator. Fig. 43. The upper surface of the 

 object is seen direct, the lower side is viewed after double reflection (see Fig. 43 b ) 

 at Si and s->, while rotation round the axis aa and reflection at A's facilitate 

 examination of all remaining portions of the object. 



a (% Full Size). 



Fig. 43. Prism Rotator, > T o. 196. 



b (magnified X 2 )- 



Sectional diagram 



of prisms . 



(xREENOUGH's Prism Rotator, in case 



The same apparatus as No. 196, but with double reflection 

 for side views, in case 



Marks Codeword 

 62. Perceptor 



75. Pereudlr 



