206 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1944 
guished. It is the opinion of both Dr. Graton and Dr. Dane that 
some present-day lenses are really capable of better resolution than 
claimed for them by their manufacturers, it having been their experi- 
ence to use objectives exhibiting superior qualities of resolution over 
those of identical medium and numerical aperture, proving that not 
only have already available lenses surpassed their theoretical limits of 
resolution, indicating that it might be possible to design objectives 
with still greater numerical apertures, but that the accepted theory 
regarding this resolution is sadly in need of revision. Dr. Lucas’s 
microscope utilizing an objective with a numerical aperture of 1.60, for 
instance, in combination with monobromnaphalene immersion fluid, 
also yields resolution up to 6,000 diameters being, like the Graton- 
Dane scope, a high-precision instrument constructed with the idea of 
maintaining absolute stability of parts. Dr. Lucas also has expressed 
doubt as to the complete validity of the generally accepted theory of 
resolution. 
In working with a high-precision ultraviolet microcamera, into 
which a tricolor filter system has been incorporated, which he has just 
recently perfected, Dr. Lucas is able to obtain a minimum magnifica- 
tion of 30,000 diameters and a maximum magnification of 60,000 diam- 
eters. With this instrument it is possible to view living cells and 
organisms, no staining or killing of organisms being necessary, and 
Dr. Lucas has succeeded in obtaining excellent photomicrographs 
(both still and motion pictures). Of special significance to industry, 
for instance, is the ability of this scope to demonstrate the size, shape, 
and reactions in motion and aflinity of the tiny particles of which 
rubber is composed under varying conditions of temperature, etc., 
while its ability to reveal living rat and mouse sarcoma and carcinoma 
cells and to demonstrate the development and behavior of the syphilitic 
organism is of far more than average interest to medical science. 
England’s Dr. J. E. Barnard has succeeded in obtaining resolution 
up to 7,500 diameters with his ultra-dark-field scope in which he uses a 
combined illuminator. In this, an outer system of glass acts as the 
immersion dark-field illuminator while the inner immersion system of 
quartz makes possible the passage of a transmitted beam of light 
through the specimen. Both condensers have the same focus, one for 
visible light, the other for ultraviolet radiation, and both can be 
stopped out at will. When, for instance, bacteria are being observed, 
immersion contact is made between the condenser and quartz slide, 
the dark-field illuminator being used, thus revealing the bacteria with 
visible light. When the dark-field illuminator is closed, however, a 
beam of ultraviolet light may be directed up through the quartz con- 
denser and focused on the bacteria. The object-glass, of course, has 
to be adjusted since it does not possess the same focus for ultraviolet 
