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initial 
On Illuminating Opake Objects for the Microscope, §c. 69 
Arr. XI.—On a new Method of Illuminating Opake Obj 
for the high powers of the Microscope:—and on a 
Achromatic Condenser ; by J... Rippeut. 
ects, 
new 
Tne front or terminal combination of the objective, is made to 
condense light upon the opake object, by sending rays of light 
from behind, through the marginal border of the lens. 
To accomplish this, a circular disk of fine plate glass, say near 
a fourth or fifth part as thick as the diameter of the lens, is bevel- 
ed on its outer margin, by grinding and polishing to an angle of 
45°, A hole is drilled through the center of the disk, of a diame- 
ter, say two-thirds, three-fourths or four-fifths (dependent upon 
the angle of aperture,) as great as that of the lens. The margin 
of this hole is also bevelled at an angle of 45°, down to a clean 
sharp edge. Both rings of bevels are on the same side of the 
glass, so that if considered as projected, the lines would cross each 
other at right angles. 
I find no insurmountable difficulty, in giving an exquisite form 
and finish to these disks. I mount and revolve the disk on a 
good rose lathe ; at the same time the grinding or polishing tool 
is revolved by an overhead motion, the spindle carrying the tool 
being mounted upon a slide rest, and admitting of a protrusive 
he. 
being thrown upon the disk, in the direction of the axis of the 
objective, from below in the direct, from above in the inverted 
Microscope, a ring of parallel rays is sent, by two successive in- 
ternal reflections from the bevelled surfaces, so that, with direc- 
ton reversed, the light traverses the outer margin of the object- 
ive, and by it is condensed upon the object in focus. ' 
I tested this method of illumination in March last, sufficiently 
to be satisfied of its great value; more especially where the ob- 
Jéctive is of very short focal distance, and where consequently, 
other means of illuminating opake objects, cannot, on account of 
the nearness of the objective to the object, be resorted to. 
New kind of Achromatic Condenser suggested. 
A larger, thicker, ‘similarly bevelled disk, with the bevels on 
pposite sides of the plate glass, and their lines of inclination co- 
Incident, would probably serve ‘as an efficient achromatic con- 
denser of parallel rays. By attaching centrally, on the side op- 
te the bevel, achromatic lenses of proper size, or a good 
doublet combination, a most valuable form of achromatic conden- 
Ser, would I think be produced, useful for general microscopic 
uination. { have not yet put the plan in practice. 
University of La, New Orleans, Oct. 4, 1852. 
