30 THE EYE 



but at the same time we of course see no more letters in 

 this than in the others. The same word also may be 

 written by a clever penman so small, that to the unassisted 

 eye it will look like a single black point. By magnifying 

 the point it might be resolved into its separate parts, so 

 that the letters and their flourishes would be distinguish- 

 able, but a further magnification would then merely enlarge 

 the scale on which the letters were seen, without bringing 

 into sight any finer parts before invisible. A similar 

 condition occurs in the microscope. Up to a certain point, 

 the picture which the object-glass throws up is such, that 

 the individual parts of the object are resolved or made 

 distinct by the eye-piece. But a limit is soon found, 

 beyond which, on account of the imperfection of the object- 

 glass, the picture which this throws up may, indeed, be 

 enlarged, but this does not render any more of its indivi- 

 dual parts visible. It is composed, as it were, of a certain 

 number of letters, which when more magnified are more 

 easily distinguished, but the increased enlargement does 

 not show any apparently simple letter to be composed of 

 two still smaller. From this cause arises the important 

 circumstance, that with a well-constructed microscope we 

 can often see far more, that is more of the individual parts 

 of the object, with a low power, than when it has been 

 much more enlarged by means of an inferior instrument. 

 Now as in all scientific investigations, every thing depends 

 upon the recognition of the individual parts and structural 

 relations, the enlargements by the microscope are only so 

 far of consequence as they enable us to do this more 

 completely. 



The limit occurs in all the instruments yet constructed 

 at an enlargement of from three to four hundred diameters, 

 and all stronger magnifying is either useless trifling or, and 



