328 THE SCIENCE OF MICROSCOPY. 



object whose details are not imnged, or whose image contains 

 apparent details fabricated by the cunning play of broken light 

 and shadow. 



Again in the attempt to interpret what is seen, the microscopist 

 has to bear in mind that a light and shadow picture does not 

 indicate the delineation of formed structure alone. For light and 

 shade are projected on the image by shapeless molecules (according 

 to size, density, aggregation, &c.) as well as by structural 

 differentiation of the formed elements of the substance examined. 

 And such delineation does not necessarily correspond with 

 transparent or opaque parts, or surface irregularities of the object, 

 or with areas indicating outlines of formed structure. The various 

 refracting density of the different constituent molecules of the 

 substance comes here into play, and many writers who describe 

 somewhat diffusely the effect of such coarse obstructions as 

 globules of air, water, oil, spirit, turpentine, gum, &c., are silent 

 upon the subject of the more subtle and less easily detected 

 influences. Thus the observer who is neither forearmed nor 

 forewarned respecting these micro -physical phenomena, but 

 simply takes every thing he sees to represent " structure," i.e., 

 formed outline, unconsciously interprets, not structure, nor any 

 corporeal element of the object, but optical effects, as if they were 

 identical with objective facts. 



But further if we omit all notice of things not clearly seen in 

 the microscope image, we exclude much occasion and motive to 

 renewal of research whether for the purpose of clearing up doubts, 

 or of fresh discovery. The microscope itself would not have 

 reached its present pitch of perfection had there not always 

 remained something which could not be clearly seen, but which 

 for that very reason excited attention and special effort to render it 

 more visible. But if the optician did not rest until he had 

 successively brought into clearer view things which less perfectly 

 constructed objectives could barely glimpse, it is no less true that 

 the microscopist has been stimulated and kept to his work by the 



