ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



435 



To the brass plate A B, having a large central opening, is attached 

 vertically a graduated semicircle, in the centre of curvature of which 

 the pinion with a milled head i 



is fitted in such a manner that it 

 may be turned round an axis at 

 right angles to the plane of the 

 semicircle. This pinion carries 

 on the other side of the semicircle 

 two sprung brass plates, between 

 which the glass slides are inserted. 

 The slides are best applied so that 

 an object lying upon them is ad- 

 justed to be in the axis of rotation, 

 and consequently suffers little or 

 no lateral displacement on rota- 

 tion. The indicator P connected 

 with the milled head, moves 

 along the graduated scale, and 

 thus gives the angle. It is ad- 

 visable for certain purposes to 

 arrange the apparatus so that the 

 object can be turned under water 

 or other liquid. This is the case, 

 for instance, in the trough appa- 

 ratus of Ebner,* which in other 

 respects is constructed on the 

 same principle as the author's. 



The same authors consider 

 that Valentin's object-stage with 

 double rotation (fig. 84) " does 

 not answer satisfactorily the pur- 

 poses required, as it affords no 

 angular determinations : it may 

 nevertheless be used in many 

 cases. It is arranged for screwing 

 to the ordinary stage, and is pro- 

 vided with adjusting screws for 

 centering. The disk Ji, i, h, I can 

 be revolved in its own plane, and 

 likewise round the horizontal 

 axis g. 



Abbe's Spectro-polarizator. t 

 — Dr. L. Dippel proposed to 

 Prof. Abbe the construction of 

 this piece of apparatus (fig. 85) 

 in order, amongst other advan- 

 tages, to obtain the benefit of 

 Eollett's Spectro-polari-Micro- 



* SB. K. K. Akad. Wiss. Wien, 1874. 

 t Bot. Centralbl., xii. (1882) pp. 284-6 

 ed., 1882, pp. 620-2 (1 fig.). 



See also Beitrand's, supra p. 415. 

 L. Dippel, ' Da3 Mikroakop,' 2nd 



2 F 2 



