ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 319 



dissecting stand f (fig- 69). It will take lenses of various sizes and 

 powers. Its stability must be doubtful, especially at the joints of 

 the arms- 

 Dissecting Microscopes with Briicke Lens.— Dissecting Micro- 

 scopes are now much in vogue on the Continent in which in place of a 



single lens, doublets in the Briicke form are employed. Fig. 70 

 shows the large dissecting Microscope of Dr. Zeiss, the general form 

 of which requires no explanatory description. The optical action is 

 shown in fig. 71, where Si is the objective and Sg the concave ocular. 

 The pencils from the object Oi O2 which after their passage 

 through the objective converge towards O2* 0* Oi* are intercepted by 

 the ocular and converted into diverging pencils which (prolonged) 

 converge at the distance of distinct vision and there form an erect 

 enlarged image of the object, Oi** 0** O2**. The objective is in 

 t Micr. Bulletin, i. (1884) p. 38 (1 fig.). 



