Microscopic Topography by Means 
of Surface Replicas 
DR. DAVID B. SCOTT, D.D.S., National Institute of Dental Research, 
National Institutes of Health, Public Health Service, Department of Health, 
Education, and Welfare, Bethesda, Maryland 
To surfaces of solid substances have been studied directly with optical mi- 
croscopes for many years. Biologists, metallographers, and petrographers 
have investigated the structures to be found on the natural surfaces of a great 
variety of objects. In addition, indications of underlying internal detail have 
been brought out on surfaces which have been created artificially by cutting 
or grinding through specimens. Almost all of the microscopy has been carried 
on with reflected light, from sources directed either obliquely or vertically to- 
ward the surfaces. Stereoscopic observation has been most popular for work 
at low power, but limitations in the depth of field afforded by glass lenses have 
made the use of magnifications over 150 X impractical. Beyond this range, vari- 
ous types of microscopes with a single objective lens have ordinarily been em- 
ployed. 
The application of stereo-photographic techniques to optical microscopy has 
also been seriously restricted by the shallow depths of field, for only a very 
small area of the image remains in the focal plane when the specimen is tilted 
to the necessary angles. As a consequence, most recording of surface detail 
has been in the form of single photographs. It has been possible, however, to 
make tridimensional measurements, like those that could be made from stereo- 
scopic photographs, directly from the specimens through the use of micro- 
scopes equipped with various types of micrometers. 
For the past fifteen years the electron microscope has found widespread use 
in the observation of surface structure. In addition to providing tremendously 
increased resolving power and magnification, the electron microscope also 
exceeds the optical microscope in the depth of field afforded by its electromagnetic 
objective lens. Due to this latter advantage, an opportunity for greatly im- 
proved stereoscopic micrography is available, and a device for tilting of speci- 
mens has been included in the basic design of almost all types of electron 
microscopes. In actual practice, however, stereoscopic electron microscopy 
has not become especially popular. This has been due chiefly to the general 
features of the electron beam which serves as the illuminant, and to those of 
specimens which are suitable for examination. The standard instruments permit 
illumination of the specimen only by transmission of electrons. The electron 
beam itself has so little penetrating power that objects of more than a few tenths 
of a micron in thickness are opaque. Since direct examination of the surfaces of 
solids has thus been virtually precluded, a method has had to be developed 
whereby the structural detail can be studied indirectly. The basic technique 
consists in reproducing the surface structure in suitably thin micro-impressions, 
known as replicas, which can be examined under the electron microscope instead 
* This is one of the papers included in the Report of the Reporter for U.S.A., Commission V 
of the International Society of Photogrammetry. 
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