44 Modern Microscopy. 



the Microscope,' that two objectives one of much greater 

 power than the other, but both having only the same 

 numerical aperture will only show the same amount of 

 detail, the higher power on a larger' scale. That is, sup- 

 posing with a J-inch objective of 1/0 N.A. certain struc- 

 ture is presented, and an J-inch objective with just double 

 the magnification, but with the same N.A., were used, 

 there would be no further power of resolution in the than 

 in the J. It therefore follows that the consideration of 

 numerical aperture must have weight in choosing an 

 objective, and here again we come to the actual limit of 

 operations proposed to be undertaken by the microscopist. 

 Although large apertures are the pride of those whose 

 ultimate microscopical ambition in life seems to be bounded 

 by the question of how the marking on Diatomacese is con- 

 structed, it is doubtful whether, for the ordinary amateur, 

 there is a 'real necessity for these large apertures. Lenses 

 of this description require a great deal of trouble and care 

 in manufacturing, and are very expensive, and if recreation 

 alone be the aim of the intending purchaser, the best series 

 of achromatic objectives which have fairly large apertures, 

 or even in some instances the medium aperture lenses com- 

 prised in the second class or second series, will be found to 

 thoroughly meet his requirements. 



The best objectives for a novice at starting would be "2- 

 inch, 1-inch, and J-inch. The 2-inch will be found extremely 

 useful for large specimens, while the 1-inch, which is con- 

 sidered the working glass of the average microscopist, will, 

 with a higher power namely, the J show him some of the 

 minuter detail which sooner or later he will wish to make 

 himself acquainted with. If more object-glasses than these 

 be required, we should recommend the J-inch as an inter- 

 mediate between the 1-inch and the J, and for a higher 

 power a yWnch oil immersion objective should be added. 

 Of course different requirements would necessitate certain 

 series of objectives, but a practical microscopical friend 

 will soon advise on this point, or any microscope manufac- 



