ON OPTICAL aUALITY OF MICROSCOPE OBJECTIVES. II 



A test image of this kind at once lays bare in all particulars the 

 whole state of correction of the microscope 5 it being of course 

 assumed that the observer knows how to observe and what to 

 look for ! 



With the aid which theory offers to the diagnosis of the various 

 aberrations, a comparison of the coloured borders of the separate 

 partial images, and an examination of their lateral separation and 

 their differences of level, as well in the middle as in the peripheral 

 zones of the entire field, suffices for an accurate definition of the 

 nature and amount of the several errors of correction, each of 

 them appearing in its own primary form. Therewith we also see 

 that which arises from aberration, properly so called, (faults of 

 focussing function) clearly separated from such imperfections, or 

 anomalies as spring from mere differences of amplification between 

 unequally converged, and unequally refracted rays ; and moreover 

 we eliminate completely all influence of the ocular on the quality 

 of the image. 



