14
intervals of time and the photographs were taken with an open stereo-
camera. Otherwise the room was of course dark. The wandering of the
particles appear very clearly at stereoscopic viewing of the photographs
and the measuring is easily done. As the photographs were taken through
glass into the water a certain calibrating of the measurements had to be
done by taking photographs of objects with known dimensions through
the glass and water. Tc determine the speed of currents cf air, very light
objects as bubbles of plast were sent up in the currents and were lighted
up by a stroboscope in front of an open stereo-camera. The speed and
direction of the current of air could then be determined as above. The
same technique was used for certain medical purposes when studying
movements of the body e. g. the movements of the foot in normal walk.
Some Investigations concerning Photogrammetry in Medicine.
Determination of Swellings.
All measurements on the soft human body are difficult to perform with
high accuracy, if such measuring device and methods are used as may
deform the surface. Photogrammetry has appeared to be useful in such
cases and has been used for research purposes to determine variations of
the dimensions of fingers and tc investigate the development of swellings
in the face at dental operations.
Fig. 4. Camera arrangement for photogrammetric deter-
mination of swellings of fingers.
In the first case (publication No. 1) the fingers were photographed with
two sterec-cameras as shows fig. No. 4. The photographs must be taken
by flash-light to eliminate the problem of synchronizing the shutters with
sufficient accuracy. The stereocomparator was used tc measure the dimen-
sions of the fingers. From diametrically opposed points on the surface of
the finger the distances between the edges of the two rulers were deter-
mined. As the breadth of the rulers was known it was then easy to calculate
the thickness of the finger. By taking photographs of the finger under
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