328 O..N. Rood on Diffraction with the Compound Microscope: 
eye-piece may be placed directly on the slit: a white space will 
be seen running across the field bordered on either side by broad 
bands of yellow, red, blue, yellow, red, green, &c.; the colors 
following in the order given above. Four orders can in this way 
be observed ; the phenomenon is exceedingly beautiful, the col- 
ors being very brilliant. By using a micrometer eye-piece, certain 
proportions which were observed by Fraunhofer to obtain among 
he bands, may be noticed. The experiment of the slits gener- 
ally succeeds better than that of the circular apertures, though if 
the slits are not perfectly regular, the bands following in an in- 
verse manner the irregularities, will be arranged in jagged lines. 
For observing the rings of color or of darkness formed within 
circular apertures or slits, gas light is preferable, though they 
may be shown by sunlight. A circular aperture, ;',th of an inch 
it two small rings of blue and red. If the eye-piece be placed 
ning parallel to its edges, and fine lines of light will project some 
distance into the shadow. When the eye-piece is removed fen 
inches the dark lines develop into colored fringes. If a piece of 
iron wire, ;4,;th of an inch in diameter, be placed as above, with 
the eye-piece at 11 inches, the centre of its shadow will be 0% 
cupied by a line of light: if the wire is as fine as 745th bf an 
inch, the eye-piece may be placed directly on it. With a larger 
size, and the eye-piece properly placed, six or seven lines of light 
and darkness can be distinctly seen; and in general the exter 
fringes will be distinct in proportion to the small size of the wit 
while the internal lines are the reverse to a limited extent. Ifa 
circular opaque body, ;';th or th of an inch be placed on 
plate of thin glass, and viewed by the eye-piece at ten gor 4 | 
besides the external fringes a circular white spot will be seen 
the centre of the shadow, as though the body had been poe 
ted. If fine chalk powder, &c., be sprinkled on the glass pia" 
and viewed by the eye-piece at ten inches, it presents an appe® 
ance of numerous fine dark lines, arranged in minute roe 
theit diameters being inversely as the size of the particles of ¢ : 
‘ For tepeating some of M. Fraunhofer’s experiments on sor 
tings, an ordinary stage micrometer, having equi-distant lines as 
at ;y,th or 545th of an inch apart, may be used.- faerie 
placed as above, shows a white space in the middle, with 
