109 



The addition of such a disk raises the price of an eye-piece by Marks 3. . 

 If it be also desired to have the eye-lens adjustable as in micrometer eye- 

 pieces (see p. 92), a further charge of Marks 6. is to be added, so that the 

 price of an eye-piece with cross-lines and adjustable eye-lens would 

 be Marks 9. higher than that of the same eye-piece without these 

 fittings. 



GEEENOUGrH's Prism and Capillary Rotators, 



These two instruments, constructed in accordance with Mr. GREENOUGH's 

 suggestions, are more especially designed to facilitate the examination, from 

 different sides in succession, of objects so small that the control of their move- 

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



The Prism-rotator, Fig. 62, a and b, serves to achieve this object in a 

 simple manner by single or multiple reflection. The upper surface of the object 

 is seen direct, the lower side is viewed after double reflection (see Fig. 62 b) at 

 s 1 and s 2 , while rotation round the axis A A and reflection at s 3 facilitate exami- 

 nation of all remaining portions of the object. 



Price : Code-word : 



No. 196: Prism-rotator with single side-view reflection, incl. case Marks 62. . Perceptor. 



The positions of "right" and "left" being reversed in consequence of the 

 single reflection at s 3 , and as this would cause inconvenience in certain cases, 

 we construct a second form of the instrument in which the objectionable 

 reversal is obviated by the addition of another prism. 



Price : Code- word : 



No. 197 : Prism-rotator with double side-vieiv reflection, incl. case Marks 75. . Percudir. 



b: (magnified 2 X)- 



Sectional diagram 



of prisms. 



a (/, Full Size). 



Fig. 62. Prism-rotator, No. 196. 



