258 ON THE THEOET OF THE illCaOSCOPE. 



proved upon objects to Tvhich the results of my observations 

 unreservedly apply, and which are said to appear ander such 

 amplification as every one vrho can understand and give an 

 account to himself of the optical conditions of such performances 

 must know to be wholly illusory. 



Postscript by the Translatoe. — In the theory of the micro- 

 scope here presented, a point of great interest is raised, in con- 

 sidering the influence which the minute structure of an object 

 exerts upon rays of light passing through it. From this point 

 of view, the chief significance of the function known as " resolving 

 power" of an objective is rightly transferred to the structural 

 condition of the object, as being the prime cause of certain optical 

 phenomena connected therewith, whilst the part played by the 

 oljective is of a more passive kind. The microscope picture, how- 

 ever true and consistent with optical law, may, indeed, in so far 

 as it suggests any false inference respecting the intimate structure 

 of an object, be spoken of as an optical illusion, although both 

 the suggestion and the false inference arise in the observer's mind 

 and cannot be charged to the objective, provided this latter be 

 correctly constructed for its own proper function. There is, 

 unfortunately, no lack of opportunity for misinterpreting optical 

 phenomena in attempting to supply, or imagine, a material cause 

 for them ! 



It is, however, clear that the first beginnings of that wonderful 

 series of refractions, dispersions, and recomposilions of light which 

 fijially result in the production of an enlarged and colourless image, 

 must be sought for in the object itself, whether the microscope 

 picture be simply a geometrical delineation or a compound of 

 negative and positive images superimposed on each other. On 

 all hands, it is agreed that suitable illumination of each 

 single object is a necessary preliminary to the most effective 

 resolution of its details. Eut until the present time this 



