CHAPTER XXI 



HOW THE GLASS USED IN MICROSCOPES IS MADE 



HAVING described all the ordinary uses of 

 the microscope and having also insisted 

 that the objectives are the most important 

 part of the instrument, there are probably many of 

 our readers who may wish to know in what manner 

 this wonderful glass differs from ordinary glass and 

 how it is made. 



Glass has been defined as a substance which, 

 during its manufacture, passes from the liquid to 

 the solid state so rapidly that no crystals are 

 formed. Usually when solids are melted and then 

 allowed to cool, they do so with the formation of 

 crystals, this may be shown in the case of sulphur 

 by melting a little and then allowing it to cool. 

 After a while, as cooling takes place a solid crust 

 will be formed on the surface of the molten sulphur. 

 If two holes are pierced in the crust and the still 

 liquid sulphur poured out, it will be found that the 

 sulphur which adhered to the vessel in which the 

 melting took place has formed beautiful needle 

 shaped crystals. 



A great amount of original work has been done 



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