/O. Microscope Construction, Use, and Care 



The microscope is probably the most indispensable ol the instru- 

 ments used in the biological sciences. Intelligent purchase and effec- 

 tive utilization of a microscope require an understanding of at least 

 the elements of its optical and mechanical construction. It is an 

 expensive instrument, built to the highest standards of precision 

 and having possibilities of performance that are not fully utilized 

 by many users. Although ha\ing some structural features that are 

 delicate or even fragile, the microscope has adequate durability to 

 give many years of useful service.* 



The function of a microscope is to produce an enlarged image 

 of an object. This is accomplished by a system of lenses. A lens may 

 be defined as a transjjarent body having at least one curved surface. 

 A simple lens, consisting of one piece of glass, may be used to illustrate 

 how a lens produces an enlarged image by bending or refracting 

 light. A ray of light coming from the object enters the uj)per j)ortion 

 of the curved face of a lens and is bent downxvard. Simihuly. a ray 

 entering the lower portion of ihe lens is bent upward. The rays which 

 pass through the lens converge and then continue as a diverging cone. 

 If a shed of paper or ground glass is placed to inicKipi the rays 

 which pass through the lens, an enlarged image of the object is pro- 

 duced on the screen. A photographic jilate can l)c |)laccd in ihc (one 

 of light and a pholograj)hi{ image obtained. A hand kiis or the 

 lens on a simple dissecting microscope produces an image on a screen 

 in this manner (Fig. Hi.l ./) . The ol))e(ti\e or loAver lens of a micro- 

 scope consists of two lo nine lenses which act as a unit U) produce 

 an image as described abc:)\e. There are certain limitations on the 

 magnification and quality of image obtainable with the objective 

 alone. Ihe primary image produced by the ol)jccti\e is iiiteicepted 



* By rourtcsy of llir Bausch X: Idiiih Ojiliral Compaiiv and llir Amciicaii Opiiial Compaiiv, 

 valual)lc siiKUX'slions for Cliaplcis lli and 17 lia\c hrcii made 1)\ nicnd)iis of lluir MafTs. I he 

 aiitlior lias drawn frci'ly on llit- (alalognc-s and sor\ ii c kallcis of the k-adins optical manufacturers. 



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