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subsoil. Hence, this equipment is not used exclusively by photogrammetrists but 
also — probably even to a larger extent — by engineers, scientists, foresters, far- 
  
Fig. 6a. The new mirror stereoscope equipment "Stereotop I" features oblique eyepieces, an 
adjustable interpupillary distance, 6-power telescopic magnifiers and minimum boxed 
dimensions, when folded. 
mers etc. who desire, or have to obtain, their information directly from aerial 
photographs. 
For this reason, these instruments must be of simple design, easy to operate 
and practically insensitive to rough or careless handling; their design must be 
such that they can be easily transported and installed and operated even in primi- 
tive surroundings. Furthermore, they must be versatile so as to be able to handle 
a variety of jobs. The new ,Stereotop" mirror stereoscope equipment attempts to 
meet these requirements. It has been developed in three stages, of which the more 
perfect stage is assembled from the simpler one by the addition of new attachments. 
The ,Stereotop T" (Fig. 6a) is a redesigned mirror stereoscope. The 6-power 
telescopic magnifiers which, however, may also be omitted, permit to pass rapidly 
from a total view to an examination of the details. For measurements of the 
parallax in the photographs, for which the need may occasionally arise, a stereo- 
meter which is not connected to the stereoscope, may be freely moved on the 
pictures. The accuracy obtained with the readings is 0.01 mm. 
If the need for extensive measurements of this nature should arise and if 
they should involve tracing work, in particular if contour lines of the terrain 
9