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To determine deformations of beams and plates under load the photo- 
graphy was made with a stereo-camera with a base cf 40 cm and the plot- 
ting was executed in a stereocomparator. 
Determination of the shape of waves etc. 
By taking stereoscopic photographs of waves of water in storm and by 
plotting the photographic material in an autograph A4 it was possible to 
make a topographic map cof the waves. 
In a similar manner the form of the whirl-pool, occurring at the inlet 
of a power generating station, was determined. A model of the power- 
station. was built in the laboratory and the whirl was photographed with 
a stereo camera, base = 40 cm. The surface of the water was made visible 
with a reflecting matter. The syncronizing of the cameras was secured 
by taking the photographs by flash-light in a dark room. 
Determination of currents in liquids and gases. 
Several experiments have shown that photogrammetry is very suitable 
to determine speed and direction of an object in motion. Film cameras can 
be used for this purpose, but the problem is to syncronize the activities 
of the cameras with enough accuracy and also to determine the inner 
orientation. This is why stereo-cameras for plates have been constantly 
used up to now. The most simple case occurs when the movement is 
slow as e. g. currents in the sea or in lakes. The methods are more compli- 
cated when the speed! is increased, but also in these cases photogrammetry 
has given good results with simple means. 
To determine the speed and direction of the current outside a coast, a 
number of floats with small electric lamps were set out in the sea at an 
interval of 20 meters and perpendicularly to the shore. On the shore were 
placed sterec-cameras and photo theodolites, the shutters of which were 
opened and shut with fixed intervals on common command. Thus the small 
lamps on the floats drew their own way on the photographie material, as 
the experiment was made by night and the photographie material was not 
blackened by other light (Fig. No. 3). By stereoscopic plotting of connected 
pairs of pictures both the speed and the direction of the current could be 
conveniently determined. 
  
Fig. 3. Stereopair of streaming water with electric lamps on floats. 
To determine movements of greater speed, like currents in liquids and 
gases, stroboscopes were used to throw light upon points in the streaming 
matter. To study the behaviour of the current in water streaming over a 
sill particles with the specific weight of water were let out in the stream. 
The water was then lighted up by stroboscope flash-lights with known