The Edge of Sight 
Human beings, always looking for 
ways to push back the limits of their 
senses, have long been dissatisfied 
with the resolving power of the human 
eye. The Romans used water droplets 
and glass to magnify things, but it 
wasn’t until the fifteenth century that 
the eye’s limitations were overcome. 
Historians believe that the first mi- 
croscope, a simple glass magnifier, 
was invented sometime about 1450 by 
an unknown entomologist as an aid 
in drawing insects. As Anton van 
Leeuwenhoek, Hans Jansen, and oth- 
ers built better microscopes, a strange 
new world populated by bizarre one- 
celled animals and tiny plants gradu- 
ally unfolded. Much later, scientists 
began to explore the structures inside 
the cells — mitochondria, Golgi bodies, 
and the endoplasmic reticulum. 
The limitations of light itself, not 
the human mind, ultimately halted the 
steady improvement of the light mi- 
croscope: the wavelength of visible 
light is simply too long to pick up 
small details, no matter how powerful 
the lens. In 1924 a physicist suggested 
that electrons bounced off a specimen 
would magnify better than light since 
the wavelength of electrons is thou- 
sands of times shorter. Shortly after- 
ward, a microscope that used electrons 
was built, and the limits of resolution 
were again pushed back. 
The American Museum of Natural 
History bought its first electron mi- 
croscope, a Cambridge S4-10, in 1972 
for $90,000. At the time it was one 
of the best microscopes in the world. 
But such is the progress of technology 
that today the S4-10 is considered ob- 
solete, bulky, and inefficient. 
This month, technicians in the Mu- 
seum’s Interdepartmental Laboratory 
will unplug and unscrew the S4-10 
and trade it in— plus $120,000 — for 
a brand-new microscope: a Cambridge 
Stereoscan 250. Most of the funds 
were provided by a grant from the 
National Science Foundation obtained 
by curators Roger Batten and Bruce 
Haugh, with the help of Robert Koest- 
ler, who manages the laboratory. The 
new scope, of which only ten have 
been built so far, is one of the finest 
of its kind. “It’s a second-generation 
instrument,” says Koestler. “Every- 
thing has been done over.” 
Like the old scope, the 250 is a 
scanning electron microscope, or 
SEM, which produces a three-dimen- 
sional picture by bombarding a speci- 
men with a shower of electrons. The 
electrons are shot down in an evac- 
uated column toward the specimen. 
Magnetic fields along the column, act- 
ing as lenses, focus the electrons into 
a narrow beam. The beam scans rap- 
idly across the specimen line after line, 
much like reading a book, and a black- 
and-white image of the surface of the 
specimen appears on a television 
screen. Because electrons, unlike light, 
have no color, SEM pictures are al- 
ways black and white. 
Electron microscopes in general are 
much more powerful than light mi- 
croscopes. The most powerful light mi- 
croscope can magnify 2,000 times, 
while the new SEM can magnify up 
to 570,000 times. To give an example, 
under a light microscope, the point 
of a pin looks surprisingly blunt. Un- 
der the SEM, however, a pinpoint be- 
comes an entire landscape. 
The Museum’s new SEM provides 
an array of fancy electronics that the 
old one lacked. The banks of vacuum 
tubes have been replaced by solid- 
state electronics, a minicomputer 
automatically adjusts the electron 
beam for greatest depth of field, and 
a new 4- by 2-inch specimen chamber 
will allow Museum scientists to look 
at specimens that were too large to 
fit into the old ‘/ 2 -inch chamber. The 
250 has twice the resolving power of 
the old S4-10, eight times the depth 
of field, and three times the magni- 
fication. Even more important for the 
Museum’s research, it can also 
achieve very low magnifications — 
about the same as a pair of thick 
eyeglasses — to look at large speci- 
mens. In addition, the Stereoscan 250 
offers such options as an “energy dis- 
persive system,” “solid-state back- 
scattering analysis,” “cathodolumi- 
nescence,” and “X-ray nucleonics.” 
The new machine will be used to 
analyze everything from diamonds 
and fossilized sea urchins to spider 
genitals. Koestler estimates that one 
hundred curators and research asso- 
ciates will use the SEM for their re- 
search projects. David Hurst Thomas, 
chairman of the Department of An- 
thropology, is studying tool assem- 
blages from an archeological site in 
Nevada. His results will appear in a 
2,000-page Museum monograph on 
the archeology of the entire Great Ba- 
sin area. Thomas used the old machine 
to look at the microscopic wear pat- 
The Hopi 
A new exhibition at the Museum, 
Hopi Kachina: Spirit of Life, will open 
February 9 in Gallery 3. The exhi- 
bition focuses on the annual kachina 
ceremonies of the Hopi, one of North 
America’s oldest continuous cultures. 
Models of Hopi villages, scenes of the 
cult ceremonies, kachinas, and other 
Hopi artifacts will be on display. 
Hopi Kachina was organized by the 
California Academy of Sciences. 
Black History 
The Museum’s African-American 
Program will observe Black History 
Month with a number of events cele- 
brating the cultural richness and di- 
versity of African and African-Ameri- 
can peoples. The programs will be 
presented in the People Center on four 
weekends, beginning Sunday, Febru- 
ary 1; among them are Music and 
Folk Traditions of East Africa, Af- 
rican Toys and Games, and African- 
American Cooking. Films on related 
subjects will also be shown during the 
weekends. All programs are free and 
will take place throughout the after- 
noon from 1:00 to 4:30. Other pro- 
grams commemorating Black History 
Month — including a multimedia trib- 
ute to singer/actor/activist Paul 
Robeson on Sunday, February 21, at 
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