ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 281 



stable, and satisfactory stand. The radius of the circular motion 

 is 4^ in., the stage is 4^ in. in diameter, the concave mirror has 

 4^ in. focal length, and the diameter of the mirror may be from 

 2J to 3 in." 



Geneva Company's Microscope. — This instrument (fig. 30), made 

 by the "Societe Genevoise pour la Construction d'Instruments de 



Fig. 30. 



Physique," has two specialities; one being the spring pincers for 

 rapidly inserting the objective, described infra p. 284, and the other 

 the mounting of the mirror. 



The mirror is attached, as shown in the woodcut, to three arms 

 articulated in such a way that " the centre of the mirror is made to 

 describe a curved line very nearly an arc of a circle, the centre of 

 which is on the object under examination. The most suitable illu- 

 mination is thus obtained very rapidly, the observer not having to 



Ser. 2.— Vol. IV. U 



