USEFUL MICROSCOPE ACCESSORIES 



137 



bulb diameter. To avoid eye fatigue, when using one of these 

 powerful tungsten lamps, it should be screened or treated with 

 frosting compound and graphite or aluminum, as suggested on 

 page 87. Two or three dippings 

 will be required to produce a 

 coating absolutely opaque. A 

 window is then made by washing 

 off a circular area with alcohol. 



Nosepieces. Objective Chang- 

 ers. In ordinary microscopic 

 investigations frequent changes 

 from one objective to another in 

 order to obtain increased magni- 

 fication are usually necessary. To 

 avoid the annoyance and loss of 

 time required to unscrew one ob- 

 jective and reinsert another, va- 

 rious devices have been suggested. 

 Those almost universally em- 

 ployed by biologists are known 

 as revolving nosepieces and are shown in Figs. 83 and 84. 

 The illustrations show their construction and operation suffi- 

 ciently well to need little comment. The nosepiece is attached 

 to the body tube of the microscope. It may accommodate 



FIG. 82. Tungsten Lamp with Con- 

 centrated Filament. 



FIG. 83. Revolving Nosepiece for 

 Three Objectives. 



FIG. 84. Dust-proof Revolving 

 Nosepiece. 



two, three or four objectives as the case may be. The 

 better type is shown in Fig. 84. It is circular and almost 

 dust-proof, while in the type shown in Fig. 83, 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 



