164 
ELEMENTARY CHEMICAL MICROSCOPY 
comment from workers with the microscope. All efforts to obtain 
this lamp by the author have thus far failed. Its description 
and applications cannot therefore be given. 
Nosepieces. Objective Changers. — In ordinary microscopic 
investigations frequent changes from one objective to another 
in order to obtain increased magnification are usually necessary. 
To avoid the annoyance and loss of time required to unscrew 
one objective and reinsert another, various devices have been 
suggested. Those almost universally employed by biologists 
are known as revolving nosepieces and are shown in Figs. 98 
and 99. The illustrations show their construction and opera¬ 
tion sufficiently well to need little comment. The nosepiece is 
attached to the body tube of the microscope. It may accom- 
Fig. 98. Revolving Nosepiece for Fig. 99 Dust-proof Revolving 
Three Objectives. Nosepiece. 
modate two, three or four objectives as the case may be. The 
better type is shown in Fig. 99. It is circular and almost dust- 
proof, while in the type shown in Fig. 98, if by chance the 
objectives are not turned under the shields dust falls upon the 
back lens combinations. Owing to the almost impossibility of 
constructing these nosepieces so that each objective will be 
properly centered when turned in place, many investigators pre¬ 
fer objective “ holders ” or “ changers ” instead of revolving 
nosepieces. Three forms of objective changers are illustrated 
in Figs. 100, loi and 102. In the case of those of the form of 
Figs. 100 and loi a flanged collar is attached to each objective. 
Pressing the levers together opens the clutch, and permits the 
objective with collar attached to be pushed in place. Upon 
releasing the levers the objective is seated and securely held. 
In the case of the Zeiss device. Fig. 102, the objective is screwed 
into the sliding block b and is pushed into the slides in the plate 
