ENGINEERING MICROSCOPES 



and finally to h , where it is viewed by the file grinding machines designed to finish- 

 eyepiece, grind regular and irregular forms of all types. 



Stereoscopic IVIicrosccpe. Since the eyes Thus in one type of grinder a drawing of the 

 are separated on the average by 64 mm, required form is made 50 times size, and the 

 each sees an object from a different view- outline is followed with the stylus of a pan- 

 point, and the images formed on the respec- tograph. A microscope is fitted to the short 

 tive retinas are correspondingly different, arm of the pantograph w^hich reduces 50/1, 

 By the stereoscopic process the brain com- and thus the microscope cross-lines trace out 

 bines the two images into one composite pic- the required form in the plane of the work, 

 turc with an accompanying sense of solidity An accuracy of at least 0.0004 in. or better 

 or depth. So the stereoscopic microscope ob- is possible. Manufacturers can provide de- 

 jectives form two images and each eye views tails on a wide range of screw and profile 

 one with an eyepiece. A prism system per- projectors and travelling microscopes for the 

 mits correct adjustments of the stereoscopic toolmaker, workshop microscopes for inspec- 

 image. For high-power microscopes two ob- tion processes, and many closely related op- 

 jectives are not practicable so that two view- tical instruments employing principles of the 

 points are secured by using the light re- optical lever and interference effects (for ex- 

 fracted by }'2 of the objective to form the ample, for the evaluation of surface flatness), 

 image for one eye, and light from the other Heating Microscope. Of both engineer- 

 half to form the other image, the division ing and chemical interest are microscopes 

 being accomplished by a prism close behind which provide necessary information con- 

 the objective. cerning the behavior of materials at elevated 



jNIeasuring Microscope. For various temperatures. In some types hot stages of 

 measurements in machine shops for example, various designs are provided directly on the 

 requiring the highest attainable accuracy, a microscope, especially for fusion analysis of 

 considerable number of microscopes of vari- crystals at relative low temperatures and 

 ous types are available which utilize glass similar observations. In other cases the heat- 

 scales or micrometer eyepieces. The Zeiss ing microscope consists of 3 principal units 

 Universal Measuring Microscope and Verti- mounted on an optical bench comprising (1) 

 cal Comparator employ glass scales for the a light source; (2) electric furnace with 

 measurement of length. A scale is viewed specimen carriage; and (3) observation and 

 with the microscope and subdivision is ef- photo-microscope. 



fected bj' means of a spiral micrometer eye- Fuel ashes, slags, ceramics, glazes and the 



piece. The master scale is graduated in 0.05 like are more or less complex mixtures of the 



in. divisions; a fixed glass scale or graticule most diverse inorganic compounds. Being 



in the microscope divides the image of one non-homogeneous substances, they do not 



division into tenths or 0.005 in. Thus small have clearly defined melting points, but 



divisions are further divided into hun- fuse and soften as they are heated and melt 



dredths, or 0.00005 in. by means of a special over a more or less wade temperature range 



graticule graduated on a separate glass disk depending upon their chemical composition 



and rotated around a center to one side of before finally reaching the liquid state. In 



the microscope axis. The microscope on a order to establish the typical softening and 



measuring machine as an optical vernier is melting behaviors small samples of the ma- 



also an optical pointer, which may take the terial to be examined are pressed into speci- 



form of a bent microscope as in the case of mens of specific shapes and the characteristic 



that used as jig borers, tool-room millers and physical changes determined as the specimen 



other precision machines, as well as in pro- is heated. 



439 



