The Advancing Poivers of Microscopic Definition. 103 



Colonel Dr. Woodward very justly remarks that the causes of these 

 false appearances have puzzled the best opticians of the age. The 

 character of these lines I have observed to vary with d liferent 

 instruments, and in inspecting Nobekt's lines, each objective seems 

 to have its own peculiar sat of spurious ones. 



The great difficulty of resolution presented to the human eye by 

 lines formed of dots is well illustrated by the following diagram : — 



If the observer shuts one eye and holds the paper at ten inches, 

 he will find that one of these hnes is better resolved at a certain 

 angle of position by turning the paper gradually so as to incline the 

 line more and more to the vertical. This simple experiment illus- 

 trates the difficulty of resolving lines (really composed of minute 

 dots), into their components. In Noherfs lines, of course no com- 

 ponent dots exist, but the spurious lines are developed in profusion. 

 The photo-picturing of these lines, however, seems to present less 

 difficulty than diatoms, which with the same degree of fineness 

 probably possess a very complicated structure. The finest Amph. 

 pellucida photographed is given, I believe, at 



NoiiERT'ri XIX Band 



92,000 lines por inch. 

 112,000 



VOL. VII. 



