MICROSCOPIC OBJECTS. 179 



the superficial magnifying powers may readily find them 

 by multiplying either of the following numbers by itself. 



FOCUS OF OBJECT-GLASS Additional 



One-third of inch. Long Eye-piece. Eye-pieces. 



Posterior pair of lenses 35 60 



Posterior and middle pairs combined . 80 140 



Three pairs of lenses combined 120 200 



ADDITIONAL OBJECT-GLASSES. 



One-seventh of an inch 225 400 



One-tenth of an inch 325 580 



One-twelfth of an inch 450 800 



One-twentieth of an inch 800 1420 



Description of a Standard Achromatic Microscope. — 

 The aim in the construction of this instrument has been 

 to obtain the most perfect and effective mounting for the 

 glasses of a microscope ; portability and expense being 

 of secondary consideration. The principles on which it 

 is built, and the mode of using it, are fully described in 

 the 'Microscopic Illustrations.' The perusal of that 

 work, with the help of the following engravings, in 

 which the latest improvements are represented, will 

 enable any person to become familiar with its capabilities 

 and to conduct satisfactorily the investigation of any 

 department of science requiring the aid of the Microscope. 



The optical part is so fully discussed by Dr. Goring in 

 his works on the Microscope, that it will be unnecessary 

 to enlarge upon it here, further than by stating that the 

 object-glasses consist of combinations of pairs of cemented 

 lenses, whereby the largest amount of penetration and 

 definition are associated with the greatest space between 

 the object and the front lens compatible with the perfect 

 correction of achromatism and spherical aberration. 



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