132 SELECTION AND USS 



of metal of proper height surrounds this hole, and forms a 

 perfect protection to the glass when the instrument is carried 

 in the pocket. The lower slip of tin may be adjusted to any 

 angle, and by turning towards the proper direction, the light 

 of any bright cloud may be reflected up through the liquid. 

 All the joints are made stiff enough to remain in position when 

 once adjusted. A watch-glass arranged in this manner holds a 

 liberal supply of liquid, so that an entire "dip" may be 

 readily examined at once. We have found this little contrivance 

 far superior to more expensive arrangements. It packs into 

 small compass, and is safely carried. 



Animalcule Cage. This forms a very excellent means 

 for holding animalcules that are too active to allow of observa- 

 tion on slides, or in watch-glasses. A good idea of its con- 

 struction may be ob- 

 tained from the en- 

 graving, where it will 

 be seen to consist of a 

 plate of metal, three 

 by one inches, to the 

 Fig. 30. ANIMALCULE CAGE. centre of which is 



fixed a short tube. In 



the upper end of this tube is fastened a beveled piece of glass, 

 and a second tube fits over the first, and has a thin glass cover 

 secured in its upper end. The animalcule is securely held 

 between the two pieces of glass, and the lower glass being 

 beveled on the edge, a drop of liquid placed on it is held be- 

 tween the two glasses by capillary attraction, and cannot spread 

 over the inside of the cage. This point is generally neglected 

 in the cheaper forms of the cage, in which the lower glass 

 is simply a plain disc burnished into the upper end of the 

 inner tube. The consequence is that when the two glasses are 

 brought together the liquid flows over the entire inside of the 

 cage, and the objects are liable to be floated out and lost. As 

 it is important that the distance of the two glasses from each 

 other should be easily and accurately regulated, the outer tube 

 should be slit, so as to make it springy. In this way it may be 

 made to move with a soft and equable motion. 



