ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 



677 



examining the quality of the work, but also in the selection of 

 material and observing its behaviour under different conditions. 



Thus the causes of the great differences in the efficiency of tools 

 used in metal-working may best be detected and studied by the 

 Microscope. The efficiency of the tool must depend not only upon 

 the quality of the steel, but also upon the way in which the edge has 

 been given to it. A tool sharpened upon a coarse grindstone is in 

 reality grooved and notched, while one that has been smoothly ground 



Fig. 119. 



Fig. 120. 



Fig. 121. 



and finished upon a hone-stone shows a straight sharp edge ; these 

 characters are well seen with the Microscope, and are also betrayed 

 by the surface of material worked by the tool. A coarsely ground 

 tool (fig. 119) produces the furrowed and ridged surface of fig. 122 ; 



Fig. 122. 



Fig. 123. 



Fig. 124. 



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one that has been ground upon an emery wheel which does not run 

 truly (fig. 120) works the surface shown in fig. 123, where the metal 

 has been torn out and not cut by the tool, while fig. 124 represents 

 the smoothly-cut surface worked by a well-finished tool (fig. 121). 



