204 § ANNUAL REPORT SMITHSONIAN INSTITUTION, 1944 
quately magnifying the image, being aided in this by the ocular which 
also serves at times to compensate for the defects in chromatic magnifi- 
cation which cannot be managed conveniently by high-power objec- 
tives, the magnification of the final image being the product of the 
magnification of the objective multiplied by the magnification of the 
ocular. An amplifier is sometimes inserted between the objective and 
ocular which causes the rays of light from the objective to diverge to 
a greater extent, thus doubling the size of the image. Magnification 
may also be improved by increasing the tube length, by increasing the 
distance from which the image is projected, and by altering the posi- 
tions of the various lenses in an adjustable objective. In general, the 
greater the magnification, the smaller will be the specimen field, but, 
as has been stressed, high powers of magnification should always be 
accompanied by equally high powers of resolution. 
As we have seen, resolution in the ordinary light microscope is 
definitely restricted by a number of interrelated elements. Even when 
monochromatic light is employed, there is always present some spheri- 
cal aberration with which to contend. True, better visibility of speci- 
mens is provided by dark-field microscopy in which the specimen is 
viewed by the high contrast of its own scattered or reflected light 
against a dark field, although in this type of illumination objects in 
the field must be well separated. Much fine detail and brilliant color 
of specimens can be observed by means of the polarization of light. 
Further, it is possible to illuminate the specimen with shorter and 
shorter wave lengths of light, the shorter the wave length of light used, 
the more of the fine detail of the specimen which can be seen, but a 
limit is reached here, also, for ordinary glass lenses are not transparent 
to ultraviolet rays. However, in the ultraviolet microscope, having a 
resolution twice that of the instruments using “visible light,” the con- 
denser, objective, and ocular are all made of quartz and, by substituting 
the photographic plate for direct observation, many excellent micro- 
graphs of numerous varieties of organisms and cellular structures can 
be made. But when viewed directly, nothing of the nature or struc- 
ture of the specimen can be ascertained; only the light scattered by the 
specimen is distinguishable, the size of the specimen being roughly 
estimated by the amount of light refracted. 
These seemingly unsurmountable obstacles of the ordinary micro- 
scopes would appear to indicate that Abbe’s law and the contention of 
physicists that “any object which is smaller than one-half the wave 
length of light by which it is illuminated cannot be seen in its true form 
or detail” are destined to remain undefied. 
REDUCTION IN THEORETICAL LIMIT OF RESOLUTION DEMONSTRATED 
But Dr. Francis F. Lucas, of the Bell Telephone Research Labora- 
tories, and Drs. Louis Cary] Graton and E. C. Dane, Jr., of the depart- 
