384 Dr. M. C. White, Diffraction in Microscopic Vision. 
Lastly, Diffraction presents an important practical difficulty 
in the microscopic investigation of common objects. ‘T'ransverse 
sections of hairs appear in the microscope surrounded with one 
or more fringes or rings. In some cases I have counted five dis- 
tinct rings. In other cases a single ring with a dark border is 
seen giving the appearance of a thick cuticle covering the hair. 
is ring, generally supposed to be the cuticle, varies in thick- 
ness with the length of the sections examined. On transverse 
sections of human hair not more than one-fourth as long as they 
are broad this ring diminishes in breadth until it appears asa 
mere film or entirely disappears. Now although I believe there 
is no doubt that the outer cells of the hair differ in structure 
ym those more internal, I seriously doubt whether this ring, 
called the cuticle, which surrounds transverse sections of hair 18 
what it is usually supposed to be. Again transverse sections 
woody fibre appear to show a laminated structure of the cell 
he first five bands of Nobert’s test, when seen in 
lar microscope, show that the coarser bands are cut much 
into the glass than the finer lines. While this instrament shows 
the first and second bands like a series of plates set UP ed 
the lines in the bands above the fifth appear only 
scratches upon the surface of the glass. I if 
observers will give us more perfect knowledge of minute struc 
tures than we at present. 
New Haven, Conn, April 3d, 1862, 
