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| The objectives
used on the universal microscope are a 1.12 dry lens, a 1.16 water immersion,
1.18 oil immersion, and a 1.25 oil immersion. The rays of light refracted
by the specimen enter the objective and are then carried up the tube in
parallel rays through 21 light bends to the ocular, a tolerance of less
than one wave length of visible light only being permitted in the core
beam, or chief ray, of illumination. Now, instead of the light rays starting
up the tube in a parallel fashion, tending to converge as they rise higher
and finally crossing each other, a ring at the ocular separated by considerable
distance as would be the case with an ordinary microscope, in the universal
tube the rays also start their rise parallel to each other but, just as
they are about to cross, a specially designed quartz prism is inserted
which serves to pull them out parallel again, another prism being inserted
each time the rays are about ready to cross. These prisms, inserted in
the tube, which are adjusted and held in alignment by micrometer screws
of 100 threads to the inch in special tracks made of magnesium (magnesium
having the closest coefficient of expansion of any metal to quartz), which
are separated by a distance of only 30 millimeters. Thus, the greatest
distance that the image in the universal is projected through any one media,
either quartz or air, is 30 millimeters instead of 160, 180, or 190 millimeters
as in the empty or air- filled tube of an ordinary microscope, the total
distance which the light rays travel zigzag fashion through the universal
tube being 449 millimeters, although the physical length of the tube itself
is 229 millimeters. It will be recalled that if one pierces a black strip
of paper or card board with the point of a needle and then brings the card
up close to the eye so that the hole is in the optic axis, a small brilliantly
lighted object will appear larger and clearer, revealing more fine detail,
than if it were viewed from the same distance without the assistance of
the card. This is explained by the fact that the beam of light passing
through the card is very narrow, the rays entering the eye, therefore,
being practically parallel, whereas without the card the beam of light
is much wider and the diffusion circles much larger. It is this principle
of parallel waves in the universal microscope and the resultant shortening
of projection distance between any two blocks or prisms plus the fact that
objectives can thus be substituted for oculars, these "oculars" being three
matched pairs of 10-millimeter, 7-millimeter, and 4-millimeter objectives
in short mounts, which make possible not only the unusually high magnification
and resolution but which serve to eliminate all distortion as well as all
chromatic and spherical aberration.
Quartz slides with especially thin quartz cover glasses are used when a tissue section or culture slant is examined, the tissue section itself also being very thin. An additional observational tube and ocular which yield a magnification of 1,800 diameters are provided so that portion of the specimen which is desired should be examined may be located and so that the observer can adjust himself more readily when viewing a section at a high magnification. The universal stage is a double rotating stage graduated through 360 degrees in quarter-minute arc divisions, the upper segment carrying the mechanical stage having a movement of 40 degrees, the body assembly which can be moved horizontally over the condenser also having an angular tilt of 40 degrees plus or minus. Heavily constructed joints and screw adjustments maintain rigidity of the microscope which ways (sic.) 200 pounds and stands 24 inches high, the bases of the scope being nickel cast steel plates, accurately surfaced, and equipped with three leveling screws and two spirit levels set at angles of 90 degrees. The coarse adjustment, a block thread screw with 40 threads to the inch, slides in a 1-1/2 dovetail which gibs directly to the pillar post. The weight of the quadruple nose piece and the objective system is taken care of by the intermediate adjustment at the top of the body tube. The stage, in conjunction with a hydraulic lift, acts as a lever in operating the fine adjustment. A 6-gauge screw having 100 threads to the inch is worked through a gland into a hollow glycerine filled post, the glycerine being displaced and replaced at will as the screw is turned clockwise or anticlockwise, allowing a 5-to-1 ratio on the lead screw. This, accordingly, assures complete absence of drag and inertia. The fine adjustment being 700 times more sensitive than that of ordinary microscopes, the length of time required to focus the universal ranges up to 1-1/2 hours which, while on first consideration, may seem a disadvantage, is after all but a slight inconvenience when compared with the many years of research and the hundreds of thousands of dollars spent and being spent in an effort to isolate and to look upon disease-causing organisms in their true form. |
